Semiconductor device

ABSTRACT

A semiconductor device with a memory unit of which the variations in the operation timing are reduced is provided. For example, the semiconductor device is provided with dummy bit lines which are arranged collaterally with a proper bit line, and column direction load circuits which are sequentially coupled to the dummy bit lines. Each column direction load circuit is provided with plural NMOS transistors fixed to an off state, predetermined ones of which have the source and the drain suitably coupled to any of the dummy bit lines. Load capacitance accompanying diffusion layer capacitance of the predetermined NMOS transistors is added to the dummy bit lines, and corresponding to the load capacitance, the delay time from a decode activation signal to a dummy bit line signal is set up. The dummy bit line signal is employed when setting the start-up timing of a sense amplifier.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application a Continuation of U.S. application Ser. No. 14/026,575,filed Sep. 13, 2013, which is a Continuation of application Ser. No.13/398,418, filed Feb. 16, 2012 which claims the benefit of JapanesePatent Application No. 2011-048053, filed Mar. 4, 2011, all of which areincorporated herein by reference in their entirety.

BACKGROUND

The present invention relates to a semiconductor device, especially totechnology which is effective when applied to a semiconductor deviceprovided with memory units, such as an SRAM.

Patent Literature 1, for example, discloses a semiconductor storagedevice which generates a sense amplifier enable signal using a dummycircuit provided with plural dummy cells. Patent Literature 2 disclosesthat, in a semiconductor storage device of a single bit line system inwhich a read operation timing is decided by operation of a replica bitline, the semiconductor storage device is configured such that a gatelength of a replica memory cell transistor coupled to the replica bitline is set to be longer than agate length of a proper memory celltransistor. Patent Literature 3 discloses a semiconductor integratedcircuit device which is provided with a first replica bit line and asecond replica bit line respectively coupled to a replica memory celland with an inverter circuit for inputting an output of the firstreplica bit line to the second replica bit line, and which generates asense amplifier enable signal by use of the divided replica bit lines.

PATENT LITERATURE

(Patent Literature 1) Japanese Patent Laid-open No. 2004-95058

(Patent Literature 2) Japanese Patent Laid-open No. 2006-31752

(Patent Literature 3) Japanese Patent Laid-open No. 2010-165415

SUMMARY

In recent years, variations between MOS transistors have appeared as asignificant issue, accompanying with the increasingly finer geometriesof a semiconductor device. Accordingly, in a memory unit (typically anSRAM (Static Random Access Memory) module) included in a semiconductordevice, for example, it becomes important to perform timing design inconsideration of the variations in an SRAM memory cell. One of suchtiming design methods is a method which sets start-up timing of a senseamplifier at the time of read using a dummy memory cell (replica memorycell) and a dummy bit line (replica bit line), for example, as disclosedby Patent Literature 1-Patent Literature 3.

However, in the method to use such a dummy memory cell, etc., it islikely that optimization of the start-up timing of the sense amplifiercannot be attained, due to the process fluctuation, etc. of the dummymemory cell itself. That is, reflecting the proper memory cell formed bya very small processing size, the dummy memory cell is formed by thesame processing size in many cases; therefore, process fluctuation, etc.tends to occur. For example, when process fluctuation occurs amongplural dummy memory cells coupled to a dummy bit line, the timing indriving the dummy bit line is different for each dummy memory cell.Consequently, there may arise the situation in which the start-up timingof the sense amplifier is too early or too late.

The present invention has been made in view of the above circumstancesand one of the purposes is to reduce the variations in operation timingin a semiconductor device provided with a memory unit. The above andother purposes and new features will become clear from description ofthe specification and the accompanying drawings of the presentinvention.

The following explains briefly an outline of typical embodiments amongthe inventions to be disclosed by the present application.

A semiconductor device according to the present invention comprises:plural word lines extending in a first direction; plural bit linesextending in the second direction intersecting the first direction; andplural memory cells arranged at intersections of the plural word linesand the plural bit lines, and configured with a circuit including afirst MIS transistor.

The semiconductor device according to the present invention furthercomprises: a sense amplifier circuit which is able to amplify a signalread from one of the plural memory cells through one of the plural bitlines, in response to an enable signal; a control circuit which is ableto generate a first signal in response to an access instruction to theplural memory cells; and a timing adjusting circuit which is able toreceive the first signal inputted and to generate a second signalserving as an origin of the enable signal, by delaying the first signal.

The timing adjusting circuit comprises a first wiring which is arrangedcollaterally with the plural bit lines and forming at least one both-waywiring, and which is able to receive the first signal transmitted at oneend and to output the second signal from the other end; and a loadcircuit including plural second MIS transistors coupled to the firstwiring.

The first wiring includes a first dummy bit line used as an outwardwiring and a second dummy bit line used as a homeward wiring, and theplural second MIS transistors are provided separately to the first dummybit line and the second dummy bit line.

The following explains briefly an effect obtained by the typicalembodiment of the inventions to be disclosed in the present application.That is, in the semiconductor device provided with a memory unit, it ispossible to reduce the variations in the operation timing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating roughly a configuration exampleof a memory unit included in the semiconductor device according toEmbodiment 1 of the present invention;

FIG. 2 is a circuit diagram illustrating a configuration example of eachmemory cell in the memory unit illustrated in FIG. 1;

FIG. 3 is a waveform chart illustrating roughly an example of operationof the memory unit illustrated in FIG. 1;

FIG. 4 is a block diagram illustrating an example of outline structureof the entire semiconductor device according to Embodiment 1 of thepresent invention;

FIG. 5 is a circuit diagram illustrating a configuration example of atiming adjusting circuit (in the column direction) of the memory unitillustrated in FIG. 1;

FIG. 6 is a circuit diagram illustrating a configuration example of atiming adjusting circuit (in the column direction), obtained bymodifying the timing adjusting circuit illustrated in FIG. 5;

FIG. 7 is a plan view illustrating a detailed layout configurationexample of a column direction load circuit of the timing adjustingcircuit illustrated in FIGS. 5 and 6;

FIG. 8( a) is a sectional view illustrating an constructional examplealong a line A-A′ illustrated in FIG. 7, and FIG. 8( b) is a sectionalview illustrating an constructional example along a line B-B′illustrated in FIG. 7;

FIG. 9 is a plan view illustrating schematic comparison of a layoutconfiguration example of a part of the word line driving circuit, thetiming adjusting circuit (in the column direction), and the memoryarray, illustrated in FIG. 1;

FIGS. 10( a) and 10(b) are plan views illustrating schematicallyrelation of the size of the timing adjusting circuit and the memoryarray in the configuration example of FIGS. 5 and 6, respectively;

FIGS. 11( a) and 11(b) are explanatory diagrams illustrating an exampleof significant difference of the timing adjusting circuit illustrated inFIG. 5 and the timing adjusting circuit illustrated in FIG. 6;

FIG. 12 is a circuit diagram illustrating a configuration example of atiming adjusting circuit (in the column direction) included in asemiconductor device according to Embodiment 2 of the present invention;

FIG. 13 is a circuit diagram illustrating another configuration exampleof a timing adjusting circuit (in the column direction) included in asemiconductor device according to Embodiment 2 of the present invention;

FIGS. 14( a), 14(b), and 14(c) are supplementary drawings illustratingload capacitance in the column direction load circuit illustrated inFIG. 12, in which FIGS. 14( a) and 14(b) are schematic diagramsillustrating the position of the load capacitance, and FIG. 14 (c) is adiagram roughly illustrating an example of voltage waveformscorresponding to the load capacitance of FIGS. 14( a) and 14(b);

FIGS. 15( a), 15(b), and 15(c) are supplementary drawings illustratingload capacitance in the column direction load circuit illustrated inFIG. 13, in which FIGS. 15( a) and 15(b) are schematic diagramsillustrating the position of the load capacitance, and FIG. 15( c) is adiagram roughly illustrating an example of voltage waveformscorresponding to the load capacitance of FIGS. 15( a) and 15(b);

FIG. 16( a) is a circuit diagram illustrating a configuration example ofa timing adjusting circuit (in the column direction) included in asemiconductor device according to Embodiment 3 of the present invention,and FIG. 16( b) is a supplementary drawing of FIG. 16( a);

FIG. 17( a) is a circuit diagram illustrating another configurationexample of a timing adjusting circuit (in the column direction) includedin a semiconductor device according to Embodiment 3 of the presentinvention, and FIG. 17( b) is a supplementary drawing of FIG. 17( a);

FIG. 18 is a circuit diagram illustrating a configuration example of atiming adjusting circuit (in the column direction) included in asemiconductor device according to Embodiment 4 of the present invention;

FIG. 19( a) is a block diagram illustrating a configuration example ofthe periphery of a read/write control circuit in the memory unitillustrated in FIG. 1 in a semiconductor device according to Embodiment5 of the present invention, and FIG. 19( b) is a circuit diagramillustrating a detailed configuration example of a read/write delaycontrol circuit illustrated in FIG. 19( a);

FIG. 20( a) is a waveform chart illustrating an example of operation atthe time of read in FIG. 19, and FIG. 20 (b) is a waveform chartillustrating an example of operation at the time of write in FIG. 19;

FIG. 21 is a circuit diagram illustrating a configuration example of atiming adjusting circuit (in the column direction) included in asemiconductor device according to Embodiment 6 of the present invention;

FIG. 22 is a circuit diagram illustrating a configuration example of atiming adjusting circuit (in the column direction) included in asemiconductor device according to Embodiment 7 of the present invention;

FIG. 23 is a circuit diagram illustrating a modified example of thecircuit diagram illustrated in FIG. 22;

FIG. 21 is a plan view illustrating a detailed layout configurationexample of a column direction load circuit of the timing adjustingcircuit illustrated in FIGS. 22 and 23;

FIG. 25 is a circuit diagram illustrating a configuration example of atiming adjusting circuit (in the column direction) included in asemiconductor device according to Embodiment 8 of the present invention;

FIG. 26 is a plan view illustrating a detailed layout configurationexample of a column direction load circuit of the timing adjustingcircuit illustrated in FIG. 25;

FIG. 27 is a circuit diagram illustrating a configuration example of atiming adjusting circuit (in the column direction) included in asemiconductor device according to Embodiment 9 of the present invention;

FIG. 28 is a circuit diagram illustrating a configuration example of atiming adjusting circuit (in the row direction) included in asemiconductor device according to Embodiment 10 of the presentinvention;

FIG. 29 is a plan view illustrating a detailed layout configurationexample of a row direction load circuit of the timing adjusting circuitillustrated in FIG. 28;

FIGS. 30( a), 30(b), and 30(c) are schematic diagrams illustratingexamples of respectively different arrangement of a timing adjustingcircuit (in the column direction) of a memory unit, in a semiconductordevice according to Embodiment 11 of the present invention;

FIGS. 31( a), 31(b), and 31(c) are schematic diagrams illustratingexamples of respectively different arrangement of a timing adjustingcircuit (in the column direction) of a memory unit which is differentfrom one illustrated in FIGS. 30 (a), 30(b), and 30(c);

FIGS. 32( a) and 32(b) are explanatory diagrams illustrating the flow ofa signal, respectively, in a case where the word line driving circuitand the timing adjusting circuit are arranged on one side of the memoryarray, and in a case where they are separately arranged on both sides ofthe memory array, in the timing adjusting circuit (in the columndirection) illustrated in FIGS. 30 and 31;

FIGS. 33( a), 33(b), and 33(c) are schematic diagrams illustratingexamples of respectively different arrangement of a timing adjustingcircuit (in the column direction) of a memory unit in a semiconductordevice according to Embodiment 12 of the present invention;

FIGS. 34( a) and 34(b) are schematic diagrams illustrating examples ofrespectively different arrangement of a timing adjusting circuit (in thecolumn direction) of a memory unit which is different from oneillustrated in FIGS. 33( a), 33(b), and 33(c); and

FIGS. 35( a) and 35(b) are schematic diagrams illustrating examples ofrespectively different arrangement of a timing adjusting circuit (in therow direction) of a memory unit in a semiconductor device according toEmbodiment 13 of the present invention.

DETAILED DESCRIPTION

When necessary for the sake of convenience in the following embodiment,the explanation will be made in divided plural sections or embodiments.However, unless otherwise specified, they are not irrelevant with eachother but they have a relationship that one is a modified example,details, and, supplementary explanation of a part or all of the other.In the following embodiments, when referring to the number of elements,etc. (including the number, a numeric value, quantity, a range, etc.),they shall be not restricted to the specific number but they may be morethan or less than the specific number, except for the case where theyare explicitly specified or clearly restricted to a specific number inprinciple.

Furthermore, in the following embodiments, it is needless to say thatthe components (including an element step, etc.) are not necessarilyessential, except for the case where they are explicitly specified orthey are considered to be essential in principle. Similarly, in thefollowing embodiments, when referring to the shape, positionalrelationship, etc. of the components, etc., they shall include what issubstantially close to or similar to the shape, etc., except for thecase where they are explicitly specified or they are considered to beclearly different in principle. This shall be equally applied to thenumeric value and the range described above.

Although not restricted in particular, circuit elements with which eachfunctional block of embodiments is configured are formed over asemiconductor substrate like a single crystal silicon by technology ofintegrated circuits, such as a well-known CMOS (complementary MOS)transistor. In the embodiments, as an example of an MISFET (MetalInsulator Semiconductor Field Effect Transistor) (abbreviated as an MIStransistor), an MOSFET (Metal Oxide Semiconductor Field EffectTransistor) (abbreviated as an MOS transistor) is employed. However, anon-oxide film is not excluded from the use as a gate insulating film.In the following drawings, a p-channel MOS transistor (PMOS transistor)is distinguished from an n-channel MOS transistor (NMOS transistor) byadding a symbol of a circle to a gate. Connection of substrate potentialof an MOS transistor is not specified in the drawings in particular.However, the method of the connection will not be restricted inparticular, as long as the MOS transistor can operate normally.

Hereinafter, embodiments of the present invention will be explained indetail with reference to the accompanying drawings. In the entirediagrams for explaining the embodiments of the present invention, thesame symbol is attached to the same component as a general rule, and therepeated explanation thereof is omitted.

Embodiment 1 Outline Structure of the Entire Memory Unit

FIG. 1 is a block diagram illustrating roughly a configuration exampleof a memory unit included in the semiconductor device according toEmbodiment 1 of the present invention. The memory unit MEMO illustratedin FIG. 1 comprises an address control circuit ADRCTL, a word linedriving circuit WD, a timing adjusting circuit (in the column direction)TMCTLB, a memory array MARY, a column selection circuit YSW, aread/write control circuit RWCTL, a write driver circuit WTD, senseamplifier circuit SA, and an input/output buffer circuit IOB. The memoryarray MARY comprises m word lines WL0-WLm extending in a firstdirection, n bit-line pairs (BL0, ZBL0)-(BLn, ZBLn) extending in asecond direction intersecting the first direction, and plural memorycells MC arranged at the intersections of m word lines and n bit-linepairs. Each bit-line pair is configured with two bit lines (for example,BL0 and ZBL0) which transmit complementary signals.

The address control circuit ADRCTL decodes (or predecodes) addresssignals A0-Aj inputted from an external address terminal of the memoryunit MEMU, in response to a decode activation signal TDEC as a trigger,and outputs row selection signals X0-Xk and column selection signalsY0-Yi. The word line driving circuit WD selects (activates) one of mword lines corresponding to the row selection signals X0-Xk. The columnselection circuit YSW selects one of n bit-line pairs corresponding tothe column selection signals Y0-Yi. The timing adjusting circuit TMCTLBis one of the main features of the present embodiment, and the detailwill be described later. The timing adjusting circuit TMCTLB outputs adummy bit line signal SDBL upon receiving the decode activation signalTDEC inputted. The read/write control circuit RWCT generates the decodeactivation signal TDEC, an internal write enable signal WE, and a senseamplifier enable signal SE, in response to the various control signals(WEN, CLK, CEN) from the external control terminal of the memory unitMEMU and the dummy bit line signal SDBL described above. The controlsignal WEN is a write enable signal which discriminates a readinstruction and a write instruction. The control signal CLK is a clocksignal used as a reference of a read/write operation. The control signalCEN is a clock enable signal which controls whether the clock signal isvalid or invalid.

The input/output buffer circuit IOB inputs a data input signal Di fromthe external data terminal of the memory unit MEMU, and transmits it tothe write driver circuit WTD. The input/output buffer circuit IOB alsoinputs an output signal from the sense amplifier circuit SA and outputsit to an external data terminal as a data output signal Do. The writedriver circuit WTD amplifies differentially the data from theinput/output buffer circuit IOB, in response to the write enable signalWE, and transmits it to a predetermined bit-line pair via the columnselection circuit YSW described above. The sense amplifier circuit SAamplifies differentially a signal pair transmitted from a predeterminedbit-line pair via the column selection circuit YSW in response to thesense amplifier enable signal SE as a trigger, and outputs it to theinput/output buffer circuit IOB.

FIG. 2 is a circuit diagram illustrating a configuration example of eachmemory cell MC in the memory unit illustrated in FIG. 1. The memory cellMC illustrated in FIG. 2 is an SRAM memory cell which is provided withfour NMOS transistors MN1-MN4 and two PMOS transistors MP1 and MP2. Asfor the NMOS transistor MN3, the gate is coupled to a word line WL andone of the source/drain is coupled to a bit line BL on the positiveelectrode side. As for the NMOS transistor MN4, the gate is coupled tothe word line WL and one of the source/drain is coupled to a bit lineZBL on the negative electrode side. The transistors MN1 and MP1 and thetransistors MN2 and MP2 configure respectively a CMOS inverter circuitbetween a power supply voltage VCC and a ground power supply voltageVSS. The two CMOS inverter circuits configure a latch circuit bycoupling the output of one side to the input of the other side. Theother one of the source/drain of the NMOS transistor MN4 is coupled tothe input of the CMOS inverter circuit (MN1, MP1) (the output of theCMOS inverter circuit (MN2, MP2)). The other one of the source/drain ofthe NMOS transistor MN3 is coupled to the input of the CMOS invertercircuit (MN2, MP2) (the output of the CMOS inverter circuit (MN1, MP1)).

<<Outline Operation of the Entire Memory Unit_(>)>

FIG. 3 is a waveform chart illustrating roughly an example of operationof the memory unit illustrated in FIG. 1. In the example of FIG. 3, atthe time when a clock signal CLK has risen, when a clock enable signalCEN is at an ‘L’ level and a write enable signal WEN is at an ‘H’ level,a read cycle (T0) is executed, and when the clock enable signal CEN isat an ‘L’ level and the write enable signal WEN is at an ‘L’ level, awrite cycle (T1) is executed. At the time when the clock signal CLK hasrisen, when the clock enable signal CEN is at an ‘H’ level, the memoryunit enters into “no operation cycle (T2)”, and neither read operationnor write operation is executed.

In the read cycle (T0), first, the read/write control circuit RWCTLshifts a decode activation signal TDEC from an ‘L’ level to an ‘H’level, in response to the rising of the clock signal CLK. The read/writecontrol circuit RWCTL outputs an internal write enable signal WE of an‘L’ level. In response to the shift to an ‘H’ level of the decodeactivation signal TDEC, the address control circuit ADRCTL generates rowselection signals X0-Xk and column selection signals Y0-Yi (Y0 isdisplayed in FIG. 3) corresponding to address signals A0-Aj. In theexample of FIG. 3, it is assumed that a word line WL0 is selected by therow selection signals X0-Xk, and a bit-line pair (BL0, ZBL0) is selectedby the column selection signals Y0-Yi. The word line driving circuit WDactivates a word line WL0 to an ‘H’ level, corresponding to the rowselection signals X0-Xk. Accordingly, stored data of each memory cell MCcoupled to the word line WL0 is read out to the corresponding bit-linepair. Here, a read signal in a bit-line pair (BL0, ZBL0) out of the readout signals is transmitted to the sense amplifier circuit SA via thecolumn selection circuit YSW.

On the other hand, in parallel to this, in response to the shift to an‘H’ level of the decode activation signal TDEC, the timing adjustingcircuit TMCTLB shifts a dummy bit line signal SDBL to an ‘H’ level,after appending a predetermined delay time (Tdly1). In response to theshift to an ‘H’ level of the dummy bit line signal SDBL, the read/writecontrol circuit RWCTL shifts a sense amplifier enable signal SE to aneffective state (′H′ level). In response to the shift to an ‘H’ level ofthe sense amplifier enable signal SE as a trigger, the sense amplifiercircuit SA amplifies the read signal of the bit-line pair (BL0, ZBL0)transmitted via the column selection circuit YSW described above. Theamplified signal is outputted to an external terminal as a data outputsignal Do via the input/output buffer circuit IOB. The word line WL0activated is deactivated, in response to the shift from an ‘H’ level toan ‘L’ level of the decode activation signal TDEC, in the present case.

Next, in the write cycle (T1), first, the read/write control circuitRWCTL shifts a decode activation signal TDEC from an ‘L’ level to an ‘H’level, in response to the rising of the clock signal CLK. The read/writecontrol circuit RWCTL outputs an internal write enable signal WE of an‘H’ level. In response to the shift to an ‘H’ level of the decodeactivation signal TDEC, the address control circuit ADRCTL generates rowselection signals X0-Xk and column selection signals Y0-Yi, and the wordline driving circuit WD activates a word line (WL0 in the present case)corresponding to the row selection signals X0-Xk. On the other hand, inparallel to this, a data input signal Di from the external terminal isinputted into the write driver circuit WTD via the input/output buffercircuit IOB. The write drive circuit WTD amplifies the input signal fromthe input/output buffer circuit IOB, in response to the shift to an ‘H’level of the internal write enable signal WE described above. The columnselection circuit YSW couples the output of the write drive circuit WTDto a bit-line pair (BL0 and ZBL0 in the present case) corresponding tothe column selection signals Y0-Yi. Accordingly, the information of thedata input signal Di is written in the selected memory cell MC. Afterthat, the word line WL0 activated is deactivated, in response to theshift from ‘H’ level to an ‘L’ level of the decode activation signalTDEC, in the present case. Accordingly, the selected memory cell MCholds the information of the data input signal Di.

<<Outline Structure of the Entire Semiconductor Device>>

FIG. 4 is a block diagram illustrating an example of outline structureof the entire semiconductor device according to Embodiment 1 of thepresent invention. FIG. 4 illustrates a semiconductor device (LSI)called an SOC (System On a Chip), etc. in which various logic circuitsand a memory circuit are formed in one semiconductor chip. Thesemiconductor device illustrated in FIG. 4 is an LSI for a mobile-phone,for example, and it comprises two processor units CPU1 and CPU2, anapplication unit APPU, a memory unit MEMU, a baseband unit BBU, and aninput/output unit IOU. The configuration example illustrated in FIG. 1is applied to the memory unit MEMU among these units.

The processor units CPU1 and CPU2 perform predetermined arithmeticprocessing based on a program. The application unit APPU performspredetermined application processing required by the mobile-phone. Thebaseband unit BBU performs predetermined baseband processingaccompanying wireless communication. The input/output unit IOU functionsas an input/output interface with the exterior. The memory unit MEMU issuitably accessed in such kind of the processing of each circuit block.In semiconductor devices, such as the SOC, the memory unit MEMU isimplemented in many cases by the automated design tool called a memorycompiler, etc., using the design data called memory IP (IntellectualProperty), etc., for example. Usually, since the optimal operationtiming also differs when the memory IP differs, it is necessary todevelop the timing adjusting circuit TMCTLB described above newly forevery memory IP. However, it is desirable to realize a timing adjustingcircuit which is usable in common by each memory IP, in the viewpoint ofthe increase in design efficiency.

<<A Detailed Circuit (1) of a Timing Adjusting Circuit (in the ColumnDirection)>>

FIG. 5 is a circuit diagram illustrating a configuration example of atiming adjusting circuit (in the column direction) of the memory unitMENU illustrated in FIG. 1. The timing adjusting circuit TMCTLBn1illustrated in FIG. 5 comprises plural (here, six pieces of) invertercircuits IV1-IV6, two dummy bit lines DBL1 and DBL2, and x-piece columndirection load circuits CLBn[1]-CLBn[x]. Here, the dummy bit lines DBL1and DBL2 have length substantially equal to the length of each bit lineBL in the memory array MARY, respectively, and are arrangedcollaterally, extending in the same direction as the extension direction(Y direction) of the bit line BL in the memory array MARY. The invertercircuits IV1-IV6 are CMOS inverter circuits, each configured with a PMOStransistor and an NMOS transistor, coupled between the power supplyvoltage VCC and the ground power supply voltage VSS.

The inverter circuits IV1 and IV2 are arranged at the input terminal ofthe dummy bit line DBL1, respectively. The inverter circuit IV1 inputsthe decode activation signal TDEC described above, and the invertercircuit IV2 inputs an output of the inverter circuit IV1 and outputs theinverted signal to the input terminal of the dummy bit line DBL1. Theinverter circuits IV3 and IV4 are arranged at the output terminal of thedummy bit line DBL1 and the input terminal of the dummy bit line DBL2,respectively. The inverter circuit IV3 inputs a signal from the outputterminal of the dummy bit line DBL1, and the inverter circuit IV4 inputsan output of the inverter circuit IV3 and outputs the inverted signal tothe input terminal of the dummy bit line DBL2. The inverter circuits IV5and IV6 are arranged at the output terminal of the dummy bit line DBL2,respectively. The inverter circuit IV5 inputs a signal from the outputterminal of the dummy bit line DBL2, and the inverter circuit IV6 inputsan output of the inverter circuit IV5 and outputs the dummy bit linesignal SDBL described above. In this way, the dummy bit lines DBL1 andDBL2 form a both-way wiring in the region of the timing adjustingcircuit TMCTLBn1 arranged close to the memory array MARY. As for theboth-way wiring here, an outward wiring is the dummy bit line DBL1, anda homeward wiring is the dummy bit line DBL2.

Each of the column direction load circuits CLBn[1]-CLBn[x] comprisesplural (here, four pieces of) NMOS transistors MNa1-MNa4 of whichsources and drains are coupled in series sequentially and gates arecoupled in common to the ground power supply voltage VSS. In each of thecolumn direction load circuits CLBn[1]-CLBn[q] as a part (for example, ahalf) of the x-piece column direction load circuits, the sources and thedrains of the NMOS transistors MNa2 and MNa3 are coupled to the dummybit line DBL1, and one end of the source/drain of the NMOS transistorsMNa1 and MNa4 (the side which is not shared by the NMOS transistors MNa2and MNa3) is open. In each of the column direction load circuitsCLBn[q+1]-CLBn[x] as the other part (for example, the other half) of thex-piece column direction load circuits, the sources and the drains ofthe NMOS transistors MNa2 and MNa3 are coupled to the dummy bit lineDBL2, and one end of the source/drain of the NMOS transistors MNa1 andMNa4 (the side which is not shared by the NMOS transistors MNa2 andMNa3) is open.

FIG. 6 is a circuit diagram illustrating a configuration example of atiming adjusting circuit (in the column direction), obtained bymodifying the timing adjusting circuit illustrated in FIG. 5. The timingadjusting circuit TMCTLBp1 illustrated in FIG. 6 is configured such thatthe x-piece column direction load circuits CLBn[1]-CLBn[x] illustratedin FIG. 5 are replaced with x-piece column direction load circuitsCLBp[1]-CLBp[x] illustrated in FIG. 6. Each of the column direction loadcircuits CLBp[1]-CLBp[x] is configured such that the plural (here, fourpieces of) NMOS transistors MNa1-MNa4 included in each of the columndirection load circuits CLBn[1]-CLBn[x] are replaced with the plural(here, four pieces of) PMOS transistors MPa1-MPa4. Unlike the NMOStransistors MNa1-MNa4 described above, the PMOS transistors MPa1-MPa4have gates coupled in common to the power supply voltage VCC.

The column direction load circuits CLBn[1]-CLBn[x], and CLBp[1]-CLBp[x]illustrated in FIGS. 5 and 6 function as load capacitance to the dummybit lines DBL1 and DBL2. Specifically, since the NMOS transistorsMNa1-MNa4 (or the PMOS transistors MPa1-MPa4) in each column directionload circuits are driven to an off state, the capacitance of thediffusion layer which forms the source and the drain of the NMOStransistors MNa2 and MNa3 (or the PMOS transistors MPa2 and MPa3) turnsinto the load capacitance to the dummy bit lines DBL1 and DBL2.Accordingly, the output signal from the inverter circuit IV2 istransmitted to the inverter circuit IV3, after being delayedcorresponding to the load capacitance generated by the column directionload circuits CLBn[1]-CLBn[q] (or CLBp[1]-CLBp[q]) and the parasiticresistance and parasitic capacitance of the dummy bit line DBL1.Similarly, the output signal from the inverter circuit IV4 istransmitted to the inverter circuit IV5, after being delayedcorresponding to the load capacitance generated by the column directionload circuits CLBn[q+1]-CLBn[x] (or CLBp[q+1]-CLBp[x]) and the parasiticresistance and parasitic capacitance of the dummy bit line DBL2.Consequently, the dummy bit line signal SDBL is obtained by delaying thedecode activation signal TDEC. More strictly, this delay time is setincluding the effect of a logic threshold value, driving ability, etc.of the inverter circuits IV1-IV6.

<<A Detailed Layout Configuration (1) of a Timing Adjusting Circuit (inthe Column Direction)>>

FIG. 7 is a plan view illustrating a detailed layout configurationexample of a column direction load circuit of the timing adjustingcircuit illustrated in FIGS. 5 and 6. FIG. 8( a) is a sectional viewillustrating a constructional example along a line A-A′ illustrated inFIG. 7, and FIG. 8( b) is a sectional view illustrating a constructionalexample along a line B-B′ illustrated in FIG. 7. As illustrated in FIGS.7 and 8, the timing adjusting circuit TMCTLBn (TMCTLBp) comprises a wellWEL, a diffusion layer DF formed in the well WEL, a polysilicon layer POformed over the well WEL with an intervening gate insulating film GS, afirst metal wiring layer M1 and a second metal wiring layer M2 formedsequentially in the upper layer, a contact layer CT in a contactprovided in an interlayer insulation layer ISL2, and a via layer V1 in avia hole provided in a interlayer insulation layer ISL2. The contactlayer CT establishes coupling between the first metal wiring layer M1and the polysilicon layer PO and coupling between the first metal wiringlayer M1 and the diffusion layer DF. The via layer V1 establishescoupling between the first metal wiring layer M1 and the second metalwiring layer M2.

In FIG. 7, two dummy bit lines DBL1 and DBL2 formed by the second metalwiring layer M2 extend collaterally toward the Y direction (theextension direction of the bit line). Eight gate wirings formed by thepolysilicon layer PO extend collaterally toward the X direction (theextension direction of the word line). The column direction load circuitCLBn (or CLBp) is formed in an intersection portion of four gate wiringsfrom the edge out of the eight gate wirings and the dummy bit line DBL1.The column direction load circuit CLBn (or CLBp) is formed also in anintersection portion of the four gate wirings concerned and the dummybit line DBL2. The column direction load circuit CLBn (or CLBp) isformed also in an intersection portion of the remaining four gatewirings and the dummy bit line DBL1, and in an intersection portion ofthe four gate wirings concerned and the dummy bit line DBL2,respectively. In each column direction load circuit, a diffusion layerDF which becomes a source or a drain is arranged on both sides of eachof the four gate wirings described above. With the use of the diffusionlayer DF, the NMOS transistors MNa1-MNa4 (or the PMOS transistorsMPa1-MPa4) described above are formed in order in the Y direction.

A space between a diffusion layer DF included in a certain columndirection load circuit and a diffusion layer DF included in anothercolumn direction load circuit is separated by an insulating layer ISL asillustrated in FIG. 8( b). Accordingly, in the example of FIGS. 5 and 7,the source or the drain of both ends in each column direction loadcircuit (the source or the drain of the transistor MNa1 (or MPa1) andthe transistor MNa4 (or MPa4)) are left open, thereby preventingcapacitance of the insulating layer ISL from being reflected in the loadcapacitance of the dummy bit line. The region composed of pluraldiffusion layers DF separated by the insulating layer ISL is called anelement active region, etc. In the configuration example illustrated inFIG. 7, four element active regions are provided respectivelycorresponding to four column direction load circuits.

Here, plural diffusion layers DF used as the source and the drain of theNMOS transistors MNa2 and MNa3 (or the PMOS transistors MPa2 and MPa3)are once coupled to a wiring in the first metal wiring layer M1 arrangedrespectively in the upper layer of each diffusion layer DF, via thecontact layer CT, and further coupled from there to the correspondingdummy bit line (DBL1 or DBL2) via the via layer V1. The eight gatewirings formed by the polysilicon layer PO are coupled in common to agate bias wiring VGL which is formed by the first metal wiring layer M1and extends toward the Y direction, via the contact layer CT. When thetiming adjusting circuit concerned is the timing adjusting circuitTMCTLBn provided with the column direction load circuit CLBn composed ofan NMOS transistor as shown in FIG. 5, the well WEL is a p type, thediffusion layer DF is an n type, and the gate bias wiring VOL issupplied with the ground power supply voltage VSS. On the other hand,when the timing adjusting circuit concerned is the timing adjustingcircuit TMCTLBp provided with the column direction load circuit CLBpcomposed of a PMOS transistor as shown in FIG. 6, the well WEL is an ntype, the diffusion layer DF is a p type, and the gate bias wiring VGLis supplied with the power supply voltage VCC.

FIG. 9 is a plan view illustrating schematic comparison of a layoutconfiguration example of a part of the word line driving circuit, thetiming adjusting circuit (in the column direction), and the memory arrayillustrated in FIG. 1. The word line driving circuit WD, the timingadjusting circuit TMCTLB, and the memory array MARY are laid out bydisposing, for example, a repeating unit with an equal pitch asillustrated in FIG. 9, in a sequentially repeated fashion toward the Ydirection. Here, in the column direction load circuit of the timingadjusting circuit TMCTLB, a gate length L2 of the gate wiring (thepolysilicon layer PO) which forms each MOS transistor described above islonger than a gate length L3 of each MOS transistor which forms eachmemory cell in the memory array MARY. Although not shown, a gate lengthof the MOS transistor which forms each inverter circuit (IV1-IV6) in thetiming adjusting circuit TMCTLB, for example, is also longer than thegate length L3 of each memory cell.

Furthermore, although not restricted in particular, the gate length L2concerned is longer than the gate length L1 of each MOS transistor whichforms the word line driving circuit WD. Usually, each MOS transistorwhich composes the word line driving circuit WD needs to have largedriving ability in order to drive a word line; therefore, the gatelength is designed short in many cases. For example, each MOS transistorin the memory array MARY is designed based on the layout rule for memorycells ordinarily applied to a memory cell. Each MOS transistor whichcomposes the word line driving circuit WD is designed based on thelayout rule for logics employed for logic circuits, such as the basebandunit BBU and the application unit APPU illustrated in FIG. 4. In thiscase, each MOS transistor which composes the timing adjusting circuitTMCTLB is also designed based on the layout rule for logics.

FIGS. 10( a) and 10(b) are plan views illustrating schematicallyrelation of the size of the timing adjusting circuit and the memoryarray in the configuration example of FIGS. 5 and 6, respectively. Asdescribed above, the length of each dummy bit line in the timingadjusting circuit TMCTLB is designed to be substantially equal to thelength of the bit line included in the memory array MARY. Accordingly,as illustrated in FIGS. 10( a) and 10(b), the size of the timingadjusting circuit TMCTLB in the Y direction will also change, followingthe number of word lines WL included in the memory array MARY (p linesin the case of FIG. 10( a), and r (r<p) lines in the case of FIG. 10(b)).

FIGS. 11( a) and 11(b) are explanatory diagrams illustrating an exampleof significant difference of the timing adjusting circuit illustrated inFIG. 5 and the timing adjusting circuit illustrated in FIG. 6. Schematiclayout configuration examples of the periphery of the memory array MARYare illustrated in FIGS. 11( a) and 11(b). In the examples, next to thememory array MARY as a reference, the timing adjusting circuit TMCTLBand the word line driving circuit WD are arranged in order in the Xdirection, and an input/output circuit block IOBK is arrangedcontiguously in the Y direction. A control circuit block CTLBK isarranged in a region which adjoins the timing adjusting circuit TMCTLBand the word line driving circuit WD in the Y direction, and whichadjoins the input/output circuit block IOBK in the X direction. Forexample, the input/output circuit block IOBK corresponds to the columnselection circuit YSW, the write driver circuit WTD, the sense amplifiercircuit SA, the input/output buffer circuit IOB, etc., illustrated inFIG. 1, and the control circuit block CTLBK corresponds to the addresscontrol circuit ADRCTL, the read/write control circuit RWCTL, etc.illustrated in FIG. 1.

In the word line driving circuit WD illustrated in FIG. 11( a), a p-typewell WEL_P is formed adjoining the timing adjusting circuit TMCTLB, andan n-type well WEL_N is formed apart from the timing adjusting circuitTMCTLB, sandwiching the p-type well WEL_P concerned. In the memory arrayMARY, an n-type well WEL_N is formed adjoining the timing adjustingcircuit TMCTLB, and a p-type well WEL_P is formed apart from the timingadjusting circuit TMCTLB, sandwiching the n-type well WEL_N concerned.In such a case, if either of the n-type well WEL_N or the p-type wellWEL_P is employed as a well of the timing adjusting circuit TMCTLB,there is almost no difference in the area efficiency. Accordingly, inthis viewpoint, no significant difference is produced by theconfiguration example illustrated in FIG. 5 and the configurationexample illustrated in FIG. 6.

On the other hand, in the word line driving circuit WD illustrated inFIG. 11( b), a p-type well WEL_P is formed adjoining the timingadjusting circuit TMCTLB, and an n-type well WEL_N is formed apart fromthe timing adjusting circuit TMCTLB, sandwiching the p-type well WEL_Pconcerned. In the memory array MARY, a p-type well WEL_P is formedadjoining the timing adjusting circuit TMCTLB, and an n-type well WEL_Nis formed apart from the timing adjusting circuit TMCTLB, sandwichingthe p-type well WEL_P concerned. In such a case, when the p-type wellWEL_P is employed as a well of the timing adjusting circuit TMCTLB, thep-type well concerned can be formed integrally with the p-type wellWEL_P of the word line driving circuit WD and the p-type well WEL_P ofthe memory array MARY. Therefore, it is possible to realize a smallarea, compared with the case where the n-type well WEL_N is employed. Inthis viewpoint, it becomes more useful to employ the configurationexample illustrated in FIG. 5 (an NMOS transistor type) than to employthe configuration example illustrated in FIG. 6 (a PMOS transistortype).

Main Effects of Embodiment 1

Up to this point, the following effects (1)-(8) are mainly obtained witheach of the configurations, by employing the semiconductor deviceaccording to the present embodiment 1. It is possible to comprehend eachof the configurations independently; accordingly, it is preferable toemploy each of the configurations which produce the effects (1)-(8)independently, or to employ a combination of some of them.

(1) On the voltage clamp of a gate of a transistor included in thetiming adjusting circuit of the semiconductor device according to thepresent embodiment 1: By employing the timing adjusting circuitdescribed above, it becomes possible to reduce the variations inoperation timing (typically start-up timing of the sense amplifier). Oneof the reasons lies in the fact that the delaying amount is set up bythe method which employs the column direction load circuit, not by thedummy memory cell method which employs a dummy memory cell possessingthe electrical property similar to that of a memory cell. In the dummymemory cell method, for example, plural dummy memory cells configured soas to store previously fixed information are coupled to a dummy bitline, and at least one dummy memory cell drive the dummy bit line, inresponse to activation of a word line (or a dummy word line). Thestart-up timing of a sense amplifier is provided mainly by the drivingtiming of the dummy bit line by the dummy memory cell. However, in amemory cell, as the finer geometries or the capacity increase advancemore, the process variations (a voltage variation and a temperaturevariation, depending on the case) become easier to occur. Accordingly,the process variations occur easily also in each dummy memory cell whichis formed reflecting the configuration of the memory cell concerned.When the process variations occur among dummy memory cells, the drivingtiming of the dummy bit line differs for every dummy memory cell,therefore, there may arise variations in the start-up timing of thesense amplifier.

On the other hand, in the method which employs the column direction loadcircuit described above, the gate of an MOS transistor is not drivendynamically as in the dummy memory cell method, but the gate of the MOStransistor is maintained at a fixed value of an off level. Accordingly,a fixed load capacitance is added to the dummy bit line in advance, andthe start-up timing of the sense amplifier is determined mainly by themagnitude of the load capacitance. The amount of variations of the loadcapacitance depends mainly on the variations of the total area of thediffusion layer DF illustrated in FIG. 7, and is easily made smallerthan the amount of variations of the driving timing of the dummy bitline by the dummy memory cell described above (in other words, theamount of variations of the current driving capacity of a dummy memorycell). Consequently, it becomes possible to reduce the variations in thestart-up timing of the sense amplifier.

(2) On the gate length of a transistor included in the timing adjustingcircuit of the semiconductor device according to the present embodiment1: By employing the timing adjusting circuit described above, it becomespossible to reduce the variations in operation timing (typicallystart-up timing of the sense amplifier). Another one of the reasons liesin the fact that, as illustrated in FIG. 9, the gate length of each MOStransistor which composes the column direction load circuit is designedlonger than the gate length of each MOS transistor in the memory cell.When the gate length is designed longer, the area of the source and thedrain is designed correspondingly larger. In a semiconductormanufacturing process, ordinarily, as the processing size becomessmaller, process variations occur easily. When the gate length becomesshorter, the size variation tends to occur easily. Accordingly, thevariations in the value of load capacitance by the column direction loadcircuit can be reduced by designing the gate length to be longer. Alsoas for each of the inverter circuits (IV1-IV6 illustrated in FIG. 5,etc.) which compose the timing adjusting circuit, it is desirable tomake the gate length of each of the MOS transistors longer than the gatelength of each of the MOS transistors in the memory cell, from aviewpoint of reducing the variations in a logic threshold value.

(3) On distributed arrangement of the column direction load circuit tothe outward wiring and the homeward wiring in the semiconductor deviceaccording to the present embodiment 1: By employing the timing adjustingcircuit described above, it becomes possible to reduce the variations inoperation timing (typically start-up timing of the sense amplifier).Further another one of the reasons lies in the fact that the columndirection load circuit is distributed in arrangement to the outwardwiring and the homeward wiring. For example, as illustrated in FIG. 5,the dummy bit line is distributed to the outward wiring (DBL1) and thehomeward wiring (DBL2), and plural column direction load circuits arearranged in each of the dummy bit lines DBL1 and DBL2.

If the column direction load circuit is arranged concentrating on oneside of the outward wiring and the homeward wiring, when variationsoccur in the structure of transistors, etc. on the concentrated side ofwiring, the variation property on the side of wiring will affect thedelay greatly. As compared with this, influence of the variations on oneside of wiring can be lessened by distributing the column direction loadcircuit to the outward wiring and the homeward wiring.

(4) On distributed arrangement of the column direction load circuit in awiring in the semiconductor device according to the present embodiment1: By employing the timing adjusting circuit described above, it becomespossible to reduce the variations in operation timing (typicallystart-up timing of the sense amplifier) Yet another one of the reasonslies in the fact that the column direction load circuit is distributedin arrangement in the Y direction. For example, in FIG. 5, when theY-direction length of the column direction load circuit becomes long,especially as a result of the increase in capacity of the memory arrayMARY, the process variations, etc. may occur depending on the positionin the Y direction. Accordingly, in FIG. 5, in each of the dummy bitline DBL1 and the dummy bit line DBL2, plural column direction loadcircuits are distributed in arrangement in the Y direction.Specifically, the column direction load circuits are configured withplural MOS transistors distributed in the Y direction. The processvariations, etc. can be averaged as a whole by employing suchdistributed arrangement.

(5) On arrangement of the inverter circuit of the semiconductor deviceaccording to the present embodiment 1: Through the distributedarrangement of the inverter circuits to the input terminal of the dummybit line DBL1, the output terminal of the dummy bit line DBL1 (the inputterminal of the dummy bit line DBL2), and the output terminal of thedummy bit line DBL2, respectively, the variations in the logic thresholdvalue, etc. of each inverter circuit can be averaged, as is the casewith the effect (4) described above.

(6) On adoption of the dummy bit line corresponding to the bit linelength of the semiconductor device according to the present embodiment1: By employing the timing adjusting circuit described above, it ispossible to set up the start-up timing of the sense amplifier optimally,corresponding to the number of word lines (bit line length). Forexample, when the number of word lines (bit line length) changesdepending on the value of capacity of the memory unit, the parasiticcapacitance, etc. of a bit line will change correspondingly. Therefore,the optimal start-up timing of the sense amplifier also differs.Accordingly, as described with reference to FIG. 10, the influence ofthe parasitic capacitance of the bit line is reflected, by following thenumber of word lines (bit line length) and changing the length of thedummy bit line. Accordingly, it is possible to set up the optimalstart-up timing of the sense amplifier to the memory unit with variousnumber of word lines (bit line length).

(7) On the configuration of a transistor included in the timingadjusting circuit of the semiconductor device according to the presentembodiment 1: By employing the timing adjusting circuit described above,it is possible to execute easily the timing adjusting in setting thestart-up timing of the sense amplifier, irrespective of the kind of thememory cell. For example, in the dummy memory cell method describedabove, since the configuration of a dummy memory cell will also changewhen the kind of a memory cell changes, it is necessary to newly developa timing adjusting circuit for each kind of the memory cell. On theother hand, the timing adjusting circuit as illustrated in FIG. 5 andothers can be employed in common irrespective of the kind of the memorycell. Specifically, when the kind of the memory cell changes, it is onlynecessary to consider the worst condition (typically, access time of thememory cell located in the end of the word line and in the end of thebit line), and just to adjust suitably the value of load capacitance ofthe column direction load circuit. In this case, without changing thebasic configuration of the layout itself illustrated in FIG. 7 forexample, it is only necessary to select suitably whether or not toprovide the via layer V1 (a coupling part between the dummy bit line andthe drain and source of each MOS transistor which composes the columndirection load circuit). Accordingly, the adjustment is easy.

(8) On application of the layout rule for logics to the timing adjustingcircuit of the semiconductor device according to the present embodiment1: By employing the timing adjusting circuit described above, it becomespossible to remove the arrangement restriction on a layout. For example,in the dummy memory cell method described above, the timing adjustingcircuit is designed by the layout rule for memory cells; accordingly, itis necessary to arrange the timing adjusting circuit inside the memoryarray (or adjoining the memory array). On the other hand, the timingadjusting circuit illustrated in FIG. 5 or others is designed by thelayout rule for logics. Therefore, it is not necessary to arrange thetiming adjusting circuit inside the memory array (or adjoining thememory array). Accordingly, it becomes possible to utilize the areaeffectively depending on the case, leading to realization of a smallarea of the semiconductor device.

Various Modified Examples of Embodiment 1

The various examples of the configuration described in Embodiment 1 isnot restricted to them and can be variously changed naturally in therange which does not deviate from the gist. For example, if it ispermissible to increase the circuit area from a viewpoint of averagingthe variations described above, it is also possible to provide the dummybit line not only as onefold both ways as illustrated in FIG. 5, but asmultifold both ways. In FIG. 5 and others, the column direction loadcircuit is provided in each of two dummy bit lines DBL1 and DBL2.However, depending on the case, it is also possible to provide thecolumn direction load circuit only in one dummy bit line. However, froma viewpoint of averaging the variations described above, it is desirableto provide the column direction load circuit in both dummy bit lines,and it is more desirable to provide them equally in both dummy bitlines. Furthermore, in FIG. 5 and others, the inverter circuits IV3 andIV4 are provided at the turning point of the dummy bit line, from aviewpoint of averaging the variations described above, etc. However, itis also possible to omit the inverter circuits concerned depending onthe case. In FIG. 5 and others, the inverter circuit of each part isprovided as two-stage configuration (for example, IV1 and IV2). However,it is also possible to change the number of stages suitably. In thiscase, from a viewpoint of making the delay time of the dummy bit lineDELI and the delay time of the dummy bit line DBL2 as equal as possible,it is desirable to make equal the signal polarity of the dummy bit lineDBL1 and the signal polarity of the dummy bit line DBL2. However, it isalso possible to set them as different polarities, depending on thecase.

Embodiment 2 A Detailed Circuit (2) of a Timing Adjusting Circuit (inthe Column Direction)

FIG. 12 is a circuit diagram illustrating a configuration example of atiming adjusting circuit (in the column direction) included in asemiconductor device according to Embodiment 2 of the present invention.The timing adjusting circuit TMCTLBn2 illustrated in FIG. 12 is amodified example of the timing adjusting circuit TMCTLBn1 illustrated inFIG. 5. The configuration example illustrated in FIG. 12 is differentfrom the configuration example illustrated in FIG. 5 in that the gatesof the NMOS transistors MNa1-MNa4 included in each of the columndirection load circuits CLBn[1]-CLBn[x] are coupled in common to thepower supply voltage VCC.

FIG. 13 is a circuit diagram illustrating another configuration exampleof a timing adjusting circuit (in the column direction) included in asemiconductor device according to Embodiment 2 of the present invention.The timing adjusting circuit TMCTLBp2 illustrated in FIG. 13 is amodified example of the timing adjusting circuit TMCTLBp1 illustrated inFIG. 6. The configuration example illustrated in FIG. 13 is differentfrom the configuration example illustrated in FIG. 6 in that the gatesof the PMOS transistors MPa1-MPa4 included in each of the columndirection load circuits CLBp[1]-CLBp[x] are coupled in common to theground power supply voltage VSS.

When the column direction load circuits CLBn[1]-CLBn[x], andCLBp[1]-CLBp[x] illustrated in FIGS. 12 and 13 are employed, unlike thecase of FIGS. 5 and 6 described above, gate insulating film capacitancewill be added as the load capacitance to the dummy bit lines DBL1 andDBL2. That is, since the MOS transistors MNa1-MNa4 (MPa1-MPa4) aredriven to an on state, the column direction load circuit adds, to thedummy bit lines DBL1 and DBL2, the gate insulating film capacitance ofthe MOS transistors MNa1-MNa4 (MPa1-MPa4) and the capacitance of thediffusion layer which composes the source and the drain of the MOStransistors MNa2 and MNa3 (MPa2 and MPa3). Usually, since the gateinsulating film capacitance is larger incapacity value than thediffusion layer capacitance, for example, when a comparatively largeload capacitance is required, or when the number of the column directionload circuits is desired to be reduced to some extent, it becomes usefulto employ the configuration example concerned.

When the configuration examples illustrated in FIGS. 12 and 13 areemployed, the layout configuration example illustrated in FIG. 7 can beapplied. In the case of FIG. 12, the power supply voltage VCC is appliedto the gate bias wiring VGL, and in the case of FIG. 13, the groundpower supply voltage VSS is applied to the gate bias wiring VGL. Whenadjusting the value of load capacitance to be added to the dummy bitline by the gate insulating film capacitance, it is only necessary toselect suitably whether or not the contact layer CT is provided forcoupling the gate bias wiring VGL and the gate wiring (polysilicon layerPO) in FIG. 7. The control here can be performed easily. It is alsopossible to employ a suitable combination of the configuration exampleof FIG. 12 (FIG. 13) and the configuration example of FIG. 5 (FIG. 6).That is, it is possible to apply the power supply voltage VCC to each ofthe MOS transistors of the column direction load circuit CLBn[1] inFIGS. 12 and 5, and to apply the ground power supply voltage VSS to eachof the MOS transistors of the column direction load circuit CLBn[q], forexample. In this case, in the layout configuration example illustratedin FIG. 7, it is only necessary to provide two gate bias wirings VGL(one for VCC, and one for VSS), and to couple one of these to the gatewiring via the contact layer CT.

FIGS. 14( a), 14(b), and 14(c) are supplementary drawings illustratingload capacitance in the column direction load circuit illustrated inFIG. 12. FIGS. 14( a) and 14(b) are schematic diagrams illustrating theposition of the load capacitance, and FIG. 14( c) is a diagram roughlyshowing an example of voltage waveforms corresponding to the loadcapacitance of FIGS. 14( a) and 14(b). FIGS. 14( a) and 14(b) illustrateexamples of cross-section structure of the NMOS transistors MNa1-MNa4 inthe column direction load circuit. In FIGS. 14 (a) and 14 (b), a gatewiring GT is formed over a p-type well WEL_P, sandwiching a gateinsulating film, and an n-type diffusion layer DF_N used as a source anda drain is formed on both sides of the gate wiring GT in the p-type wellWEL_P.

FIG. 14( a) illustrates the case where the ground power supply voltageVSS is applied to the gate wiring GT, and the present case correspondsto the case illustrated in FIG. 5. In the present case, a channel is notformed beneath the gate of the NMOS transistor, and the dummy bit line(here DBL1) coupled to the diffusion layer DF_N used as the source orthe drain can see diffusion layer capacitance (pn junction capacitance)Csb (or Cdb) between the diffusion layer DF_N concerned and the p-typewell WEL_P. FIG. 14( b) illustrates the case where the power supplyvoltage VCC is applied to the gate wiring GT, and the present casecorresponds to the case illustrated in FIG. 12. In the present case, achannel NCH is formed beneath the gate of the NMOS transistor.Accordingly, the dummy bit line DBL1 coupled to the diffusion layer DF_Nused as the source, for example, can see diffusion layer capacitance Csbbetween the diffusion layer DF_N (source) and the p-type well WEL_P, andin addition, gate insulating film capacitance Cg, pn junctioncapacitance Ccb between the channel NCH and the p-type well WEL_P, anddiffusion layer capacitance Cdb between the diffusion layer DF_N (drain)and the p-type well WEL_P. The gate insulating film capacitance Cg isthe sum total of gate-source capacitance Csg and gate-drain capacitanceCdg.

Accordingly, when the dummy bit line DBL1 shifts from an ‘H’ level to an‘L’ level, a delay (a gentle change of a waveform) as illustrated inFIG. 14( c) occurs depending on the kind of the load capacitance. First,in the case of FIG. 14( a), the value of the load capacitance is givenby the sum of the parasitic capacitance Cdbl1 of the dummy bit line DBL1and the diffusion layer capacitance Csb (or Cdb), totaling to “Cdbl1+Csb(Cdb).” Therefore, as illustrated in FIG. 14( c), the voltage waveformof the dummy bit line DBL1 exhibits a more gentle change, as comparedwith the case where the value of the load capacitance is given by onlythe parasitic capacitance Cdbl1. Next, in the case of FIG. 14( b), thevalue of load capacitance is given by the sum total“Cdbl1+Csb+Cdb+Ccb+Cg.” Therefore, as illustrated in FIG. 14( c), thevoltage waveform of the dummy bit line DBL1 exhibits a furthermoregentle change, as compared with the case of FIG. 14( a). However, thevoltage waveform of the dummy bit line DBL1 exhibits a furthermoregentle change than in the case of FIG. 11( a) bordering on a certainvoltage level, because, in the transition period of the voltage of thedummy bit line DBL1, the channel NCH (that is, Cdb+Ccb+Cg) is notgenerated in the period where the voltage level of the dummy bit lineDBL1 is near an ‘H’ level to some extent.

FIGS. 15( a), 15(b), and 15(c) are supplementary drawings illustratingload capacitance in the column direction load circuit illustrated inFIG. 13, in which FIGS. 15( a) and 15(b) are schematic diagramsillustrating the position of the load capacitance, and FIG. 15( c) is adiagram roughly showing an example of voltage waveforms corresponding tothe load capacitance of FIGS. 15( a) and 15(b). FIGS. 15( a) and 15(b)illustrate examples of cross-section structure of the PMOS transistorsMPa1-MPa4 in the column direction load circuit. In FIGS. 15( a) and15(b), a gate wiring GT is formed over an n-type well WEL_N, sandwichinga gate insulating film, and a p-type diffusion layer DF_P used as asource and a drain is formed on both sides of the gate wiring GT in then-type well WEL_N.

FIG. 15( a) illustrates the case where the power supply voltage VCC isapplied to the gate wiring GT, and the present case corresponds to thecase illustrated in FIG. 6. In the present case, a channel is not formedbeneath the gate of the PMOS transistor, and the dummy bit line (hereDBL1) coupled to the diffusion layer DF_P used as the source or thedrain can see diffusion layer capacitance (pn junction capacitance) Csb(or Cdb) between the diffusion layer DF_P concerned and the n-type wellWEL_N. FIG. 15( b) illustrates the case where the ground power supplyvoltage VSS is applied to the gate wiring GT, and the present casecorresponds to the case illustrated in FIG. 13. In the present case, achannel PCH is formed beneath the gate of the PMOS transistor.Accordingly, the dummy bit line DBL1 coupled to the diffusion layer DF_Pused as the source, for example, can see diffusion layer capacitance Csbbetween the diffusion layer DF_P (source) and the n-type well WEL_N, andin addition, gate insulating film capacitance Cg, pn junctioncapacitance Ccb between the channel PCH and the n-type well WEL_N, anddiffusion layer capacitance Cdb between the diffusion layer DF_P (drain)and the n-type well WEL_N. The gate insulating film capacitance Cg isthe sum total of gate-source capacitance Cgs and gate-drain capacitanceCgd.

Accordingly, when the dummy bit line DBL1 shifts from an ‘H’ level to an‘L’ level, a delay (a gentle change of a waveform) as illustrated inFIG. 15( c) occurs depending on the kind of the load capacitance. First,in the case of FIG. 15( a), the value of the load capacitance is givenby the sum of the parasitic capacitance Cdbl1 of the dummy bit line DBL1and the diffusion layer capacitance Csb (or Cdb), totaling to “Cdbl1+Csb(Cdb).” Therefore, as illustrated in FIG. 15( c), the voltage waveformof the dummy bit line DBL1 exhibits a more gentle change, as comparedwith the case where the value of the load capacitance is given by onlythe parasitic capacitance Cdbl1. Next, in the case of FIG. 15( b), thevalue of load capacitance is given by the sum total“Cdbl1+Csb+Cdb+Cob+Cg.” Therefore, as illustrated in FIG. 15( c), thevoltage waveform of the dummy bit line DBL1 exhibits a furthermoregentle change, as compared with the case of FIG. 15( a). However, thevoltage waveform of the dummy bit line DBL1 exhibits a change from agreatly gentle change to a less gentle change observed in the case ofFIG. 15( a), bordering on a certain voltage level, because, in thetransition period of the voltage of the dummy bit line DBL1, the channelPCH (that is, Cdb+Ccb+Cg) disappears in the period where the voltagelevel of the dummy bit line DBL1 approaches an ‘L’ level to some extent.

In this way, when the column direction load circuit which utilizes thegate insulating film capacitance as the load capacitance is employed,how the load capacitance is seen is different, depending on thecombination of the transition direction of the voltage level of thedummy bit line DBL1 and the conductive type of the MOS transistor of thecolumn direction load circuit. For example, when an NMOS transistor isemployed, in the transition of the voltage level of the dummy bit lineDBL1 from an ‘H’ level to an ‘L’ level, the gate insulating filmcapacitance cannot be seen in the early stage, however, in thetransition from an ‘L’ level to an ‘H’ level, the gate insulating filmcapacitance can be seen in the early stage. On the contrary, when a PMOStransistor is employed, in the transition of the voltage level of thedummy bit line DBL1 from an ‘H’ level to an ‘L’ level, the gateinsulating film capacitance can be seen in the early stage, however, inthe transition from an ‘L’ level to an ‘H’ level, the gate insulatingfilm capacitance cannot be seen in the early stage. Usually, it is moredesirable to employ the combination in which the gate insulating filmcapacitance can be seen in the early stage of the transition.

As described above, it is possible to easily support even a case where alarge value of load capacitance is required for example, by employingthe semiconductor device of the present embodiment 2. In the presentembodiment 2, either one of the PMOS transistor or the NMOS transistoris employed as the column direction load circuit. However, it is alsopossible to realize a configuration so that both may be employed,depending on the case. That is, a p-type well and an n-type well areboth formed in the timing adjusting circuit, and a part of the columndirection load circuit is configured with the NMOS transistors, and theother part is configured with the PMOS transistors. In this case,although the circuit area may increase, it becomes possible to averagethe degree of how the gate insulating film capacitance can be seen,during the transition period of the voltage level of the dummy bit line.

Embodiment 3 A Detailed Circuit (3) of a Timing Adjusting Circuit (inthe Column Direction)

FIG. 16( a) is a circuit diagram illustrating a configuration example ofa timing adjusting circuit (in the column direction) included in asemiconductor device according to Embodiment 3 of the present invention,and FIG. 16( b) is a supplementary drawing of FIG. 16( a). The timingadjusting circuit TMCTLB3 illustrated in FIG. 16( a) is a modifiedexample of the timing adjusting circuit TMCTLBn1 illustrated in FIG. 5.The timing adjusting circuit TMCTLB3 illustrated in FIG. 16( a) differsfrom the timing adjusting circuit TMCTLBn1 illustrated in FIG. 5 in thatthe column direction load circuits are changed into variable columndirection load circuits VCLBn[1]-VCLBn[x].

The variable column direction load circuit VCLBn[1]-VCLBn[x] areprovided with NMOS transistors MNa1-MNa4 as is the case with FIG. 5;however, unlike the case with FIG. 5, each gate voltage of the NMOStransistors MNa1-MNa4 can be set up suitably. For this reason, in FIG.16( a), a load capacitance setting circuit CLCTL including latchcircuits LTa and LTb is provided further. In the present configuration,the latch circuit LTa latches a load capacitance setting signal Sainputted separately, and controls the gate voltage of the NMOStransistor MNa1, and the latch circuit LTb latches a load capacitancesetting signal Sb inputted separately, and controls the gate voltage ofthe NMOS transistors MNa2-MNa4 in common.

In the present configuration example, as illustrated in FIG. 16( b),first, when the load capacitance setting signals (Sa, Sb) are set at(‘1’, ‘0’) (‘1’: a VCC level, ‘0’: a VSS level), the NMOS transistorMNa1 is set to an on state, and the NMOS transistors MNa2-MNa4 are setto an off state, respectively. Consequently, the load capacitance of thedummy bit lines DBL1 and DBL2 by the column direction load circuit isgiven mainly by the sum total of the gate insulating film capacitance ofthe NMOS transistor MNa1 and the diffusion layer capacitance of thesource and the drain of the NMOS transistors MNa1-MNa3. Next, when theload capacitance setting signals (Sa, Sb) are set at (‘0’, ‘0’), theNMOS transistors MNa1-MNa4 are set to an off state. Consequently, theload capacitance of the dummy bit lines DBL1 and DBL2 by the columndirection load circuit is given by the sum total of the diffusion layercapacitance of the source and the drain of the NMOS transistors MNa2 andMNa3. In the present case, since the value of load capacitance becomessmaller as compared with the case of the load capacitance settingsignals (Sa, Sb) (‘1’, ‘0’) (defined as a case of standard setup), thestart-up timing of a sense amplifier is set up a little early.

Next, when the load capacitance setting signals (Sa, Sb) are set at(‘0’, ‘1’), the NMOS transistor MNa1 is set to an off state, and theNMOS transistors MNa2-MNa4 are set to an on state, respectively.Consequently, the load capacitance of the dummy bit line DBL1 and DBL2by the column direction load circuit is given mainly by the sum total ofthe gate insulating film capacitance of the NMOS transistors MNa2-MNa4and the diffusion layer capacitance of the source and the drain of theNMOS transistors MNa2-MNa4. In the present case, since the value of loadcapacitance becomes larger as compared with the above described case ofthe standard setup, the start-up timing of the sense amplifier is set uplater. Finally, when the load capacitance setting signals (Sa, Sb) areset at (‘1’, ‘1’), the NMOS transistors MNa1-MNa4 are set to an onstate. Consequently, the load capacitance of the dummy bit line DBL1 andDBL2 by the column direction load circuit is given mainly by the sumtotal of the gate insulating film capacitance of the NMOS transistorsMNa1-MNa4 and the diffusion layer capacitance of the source and thedrain of the NMOS transistors MNa1-MNa4. In the present case, since thevalue of load capacitance becomes still larger as compared with the caseof the load capacitance setting signals (Sa, Sb) (‘0’, ‘1’) describedabove, the start-up timing of the sense amplifier are set up stilllater.

The information on the load capacitance setting signals Sa and Sb may bestored in advance on a non-volatile memory, when the semiconductordevice is provided with the non-volatile memory, or the information maybe set permanently by means of a fuse, etc., or, when the semiconductordevice is provided with a setup mode, the information may be dynamicallychanged via various circuit units in the semiconductor device or via anexternal terminal in the setup mode concerned. For example, when testingmemory units, such as an SRAM, there is a case where one wishes to delaythe start-up timing of a sense amplifier temporarily. In such a case,the configuration which can be changed dynamically is desirable. In FIG.16( a), the variable setup is realized by the combination of one MOStransistor (MNa1) and three MOS transistors (MNa2-MNa4). However, itshould be understood that the combination is not restricted to the casebut can be changed suitably. However, by assigning different numbers ofMOS transistors to each of the load capacitance setting signals, asshown in FIG. 16( a), it becomes possible to realize the variable setupof several steps (four steps in the present example) with which thevalue of load capacitance can be varied with sufficient balance.

FIG. 17( a) is a circuit diagram illustrating another configurationexample of a timing adjusting circuit (in the column direction) includedin a semiconductor device according to Embodiment 3 of the presentinvention, and FIG. 17( b) is a supplementary drawing of FIG. 17( a).The timing adjusting circuit TMCTLB4 illustrated in FIG. 17 (a) is amodified example of the timing adjusting circuit TMCTLBn1 illustrated inFIG. 5. The timing adjusting circuit TMCTLB4 illustrated in FIG. 17( a)is different from the timing adjusting circuit TMCTLBn1 illustrated inFIG. 5 in that the inverter circuits IV2 and IV4 illustrated in FIG. 5are changed into variable inverter circuits VIV2 and VIV4.

In the configuration of each of the variable inverter circuits VIV2 andVIV4, a pull-up PMOS transistor MP10 is coupled between the power supplyvoltage VCC and an output node, and pulldown NMOS transistors MN10 a,MN10 b, and MN10 c are inserted in parallel between the output node andthe ground power supply voltages VSS. The PMOS transistor MP10 and theNMOS transistors MN10 a, MN10 b, and MN10 c are coupled to an input nodein common at respective gates. Here, the NMOS transistors MN10 a, MN10b, and MN10 c are coupled to the ground power supply voltage VSSrespectively via NMOS transistors MN11 a, MN11 b, and MN11 c, each ofwhich serves as a switch. Accordingly, the driving ability of thevariable inverter circuit VIV can be set up suitably by turning on andoff the switch concerned.

Therefore, in FIG. 17 (a), a load capacitance setting circuit CLCTLincluding latch circuits LTc and LTd is further provided. In the presentconfiguration, the latch circuit LTc latches a load capacitance settingsignal Sc inputted separately, and controls on/off of the NMOStransistor MN11 a, and the latch circuit LTd latches a load capacitancesetting signal Sd inputted separately, and controls on/off of the NMOStransistor MN11 b. The NMOS transistor MN11 c is fixed to an on state bythe power supply voltage VCC applied to the gate thereof. Here, thecurrent driving capacity of the NMOS transistors MN11 a, MN11 b, andMN11 c, each of which serves as a switch, is set up identically. Thecurrent driving capacity of the pulldown NMOS transistor MN10 b is setto be greater than the current driving capacity of the NMOS transistorMN10 a.

In this case, as illustrated in FIG. 17( b), first, when the loadcapacitance setting signals (Sc, Sd) are set at (‘1’, ‘0’) (‘1’: a VCClevel, ‘0’: a VSS level), the NMOS transistor MN10 a is added to theNMOS transistor MN10 c as an effectual pulldown transistor. Next, whenthe load capacitance setting signals (Sc, Sd) are set at (‘0’, ‘0’), theeffectual pulldown transistor is only the NMOS transistor MN10 c.Consequently, the current driving capacity of the variable invertercircuit VIV becomes smaller than the case of the load capacitancesetting signals (Sc, Sd)=(‘1’, ‘0’) described above (defined as thestandard setup). Therefore, the start-up timing of the sense amplifierwill be set up later.

Next, when the load capacitance setting signals (Sc, Sd) are set at(‘0’, ‘1’), the NMOS transistor MN10 b is added to the NMOS transistorMN10 c, as the effectual pulldown NMOS transistors. Consequently, thecurrent driving capacity of the variable inverter circuit VIV becomeslarger than the case of the standard setup described above. Therefore,the start-up timing of the sense amplifier ill be set up a littleearlier. Finally, when the load capacitance setting signal (Sc, Sd) isset at (‘1’, ‘1’), the NMOS transistors MN10 a and MN10 b are added tothe KMOS transistor MN10 c, as the effectual pulldown transistors.Consequently, the current driving capacity of the variable invertercircuit VIV becomes still larger than the case of the load capacitancesetting signal (Sc, Sd)=(‘0’, ‘1’) described above. Therefore, Thestart-up timing of the sense amplifier will be set up still earlier. Inthe present example, the configuration of the pulldown side is madevariable, assuming the case where the start-up timing of the senseamplifier is set by the shift from an ‘H’ level to an ‘L’ level of thedummy bit lines DBL1 and DBL2. However, when the shift from an ‘L’ levelto an ‘H’ level is employed, it is sufficient that the configuration ofthe pull-up side is made variable. Naturally, the variable method of thecurrent driving capacity is not limited to the configuration exampleillustrated in FIG. 17 (a), but can be changed suitably.

As described above, by employing the semiconductor device according tothe present embodiment 3, it is possible to realize the configuration inwhich the start-up timing of the sense amplifier can be adjusted bymeans of various kinds of variable setup. For example, it is possible tofacilitate a test and to realize the trimming responding tomanufacturing variations, etc., as described above. As illustrated inFIG. 12 and others, depending on the case, it becomes possible to adjustthe value of load capacitance after manufacture, without adjustment ofthe existence or nonexistence of the contact layer CT illustrated inFIG. 7, which would be performed in the design and the manufacturingstage according to the kind of a memory unit, etc.

Embodiment 4 A Detailed Circuit (4) of a Timing Adjusting Circuit (inthe Column Direction)

FIG. 18 is a circuit diagram illustrating a configuration example of atiming adjusting circuit (in the column direction) included in asemiconductor device according to Embodiment 4 of the present invention.The timing adjusting circuit TMCTLBn3 illustrated in FIG. 18 is amodified example of the timing adjusting circuit TMCTLBn1 illustrated inFIG. 5. FIG. 5 illustrates the circuit diagram of the timing adjustingcircuit TMCTLBn1 in which the values of load capacitance by the columndirection load circuits CLBn[1]-CLEn[x] are the same. However, thevalues of load capacitance may not be necessarily the same. For example,as illustrated in FIG. 18, it is possible to make small the value ofload capacitance of the column direction load circuits CLBn′[q] andCLBn′[q+1] located in the output terminal of the dummy bit line DELI andthe input terminal of the dummy bit line DBL2, respectively, as comparedwith the value of load capacitance of the column direction load circuitsCLBn[1] and CLBn[x] located in the input terminal of the dummy bit lineDBL1 and the output terminal of the dummy bit line DBL2, respectively.

In FIG. 18, the column direction load circuits CLBn′[q] and CLBn′[q+1]are configured with plural (here, four pieces of) NMOS transistorsMNb1-MNb4 coupled in series, as is the case with the column directionload circuits CLBn[1] and CLBn[x]. However, unlike the column directionload circuits CLBn[1] and CLEn[x], only a common connecting node (asource or drain) of the NMOS transistors MNb2 and MNb3 is coupled to thecorresponding dummy bit line (DBL1 or DBL2). The same effect as in thecase of Embodiment 1 can be obtained by the present configuration aswell.

Embodiment 5 Details of a Read/Write Control Circuit

FIG. 19( a) is a block diagram illustrating a configuration example ofthe periphery of a read/write control circuit in the memory unitillustrated in FIG. 1 in a semiconductor device according to Embodiment5 of the present invention, and FIG. 19( b) is a circuit diagramillustrating a detailed configuration example of a read/write delaycontrol circuit illustrated in FIG. 19( a). FIG. 20( a) is a waveformchart illustrating an example of operation at the time of read in FIG.19, and FIG. 20( b) is a waveform chart illustrating an example ofoperation at the time of write in FIG. 19.

A read/write control circuit RWCTL illustrated in FIG. 19( a) isprovided with a decode activation signal generating circuit TDECGEN anda read/write delay control circuit RWDLYCTL. As illustrated in FIGS. 20(a) and 20(b), the decode activation signal generating circuit TDECGENactivates a decode activation signal TDEC in response to the clocksignal CLK, etc. The word line driving circuit WD activates apredetermined word line WL in response to the rising of the decodeactivation signal TDEC. The timing adjusting circuit TMCTLB outputs adummy bit line signal SDBL by imparting a predetermined delay time(Tdly1) to the decode activation signal TDEC, as described above.

When a read operation (here WE=‘0’) is specified by the internal writeenable signal WE, the read/write delay control circuit RWDLYCTLactivates the sense amplifier enable signal SE in response to the dummybit line signal SDBL, as illustrated in FIG. 20( a). The sense amplifiercircuit SA performs an amplifying operation in response to the senseamplifier enable signal SE activated. In this case, the transition speed(the drawing-out speed of a charge from the state precharged at an ‘H’level in advance) of the proper bit-line pair (BL, ZBL) changesdepending on the numberof the word lines WL (the bit line length).Therefore, it becomes useful to employ the timing adjusting circuitTMCTLB described above.

When a write operation is specified by the internal write enable signalWE (here WE=‘1’), the read/write delay control circuit RWDLYCTLactivates a write-mode word line pull-down signal BACKW in response tothe dummy bit line signal SDBL after the predetermined delay time(Tdly2), as illustrated in FIG. 20( b). The decode activation signalgenerating circuit TDECGEN deactivates the decode activation signalTDEC, after the predetermined period set in advance, when the readoperation is specified by the internal write enable signal WE, asillustrated in FIG. 20( a). The decode activation signal generatingcircuit TDECGEN deactivates the decode activation signal TDEC inresponse to the write-mode word line pull-down signal BACKW activated,when the e operation specified by the internal write enable signal WE,as illustrated in FIG. 20( h). As illustrated in FIGS. 20( a) and 20(b),the word line driving circuit WD deactivates the predetermined word lineWL in response to the falling of the decode activation signal TDEC.

As illustrated in FIG. 20( b), when writing storage information which isopposite to the present storage information in the memory cell MC, theinverting speed at the memory nodes (MEMT, MEML) in the memory cell MCchanges depending on the number of the word lines WL (the bit linelength). Accordingly, at the time of write, it is desirable to adjustthe timing of deactivating the word line WL, corresponding to the numberof the word lines WL (the bit line length). Accordingly, in the presentembodiment 5, not only the start-up timing of the sense amplifier butthe timing of deactivating the word line WL at the time of write isadjusted by means of the timing adjusting circuit TMCTLB describedabove.

The read/write delay control circuit RWDLYCTL can be realized with twocontrol-switch-equipped inverter circuits CIV1 and CIV2 and a delaycircuit block IVBK configured with plural stages of inverter circuits,for example, as illustrated in FIG. 19( b). Each of thecontrol-switch-equipped inverter circuits CIV1 and CIV2 comprises PMOStransistors MP20 and MP21 coupled in series between the power supplyvoltage VCC and an output node (that is, the pull-up side), and NMOStransistors MN20 and MN21 coupled in series between the ground powersupply voltage VSS and the output node (that is, the pulldown side). ThePMOS transistor MP20 and the NMOS transistor MN20 form a CMOS invertercircuit, and the PMOS transistor MP21 and the NMOS transistor MN21function as a control switch for controlling activation and deactivationof the CMOS inverter circuit concerned.

In the control-switch-equipped inverter circuit CIV1, when a readoperation is specified by the internal write enable signal WE (WE=‘0’),the control switch is set to on, the CMOS inverter circuit inputs andinverts a dummy bit line signal SDBL (here the inverted signal thereof)and outputs a sense amplifier enable signal SE to the output node. Inthe inverter circuit CIV1, when a write operation is specified by theinternal write enable signal WE (WE=‘1’), the control switch is set tooff and the output node of the CMOS inverter circuit is brought to ahigh-impedance state. In this case, although not shown, the output nodeconcerned is driven to the level of the ground power supply voltage VSSby a pulldown switch, etc.

On the other hand, in the control-switch-equipped inverter circuit CIV2,when a write operation is specified by the internal write enable signalWE (WE=‘1’), the control switch is set to on. In this case, the dummybit line signal SDBL (here the inverted signal thereof) is inputted intothe CMOS inverter circuit after the delay (Tdly2 in FIG. 20( b)) by thedelay circuit block IVBK. The CMOS inverter circuit inverts the inputsignal concerned, and outputs a write-mode word line pull-down signalBACKW to the output node. In the control-switch-equipped invertercircuit CIV2, when a read operation is specified by the internal writeenable signal WE (WE=‘0’), the control switch is set to off and theoutput node of the CMOS inverter circuit is brought to a high-impedancestate. In this case, although not shown, the output node concerned isdriven to the level of the ground power supply voltage VSS by a pulldownswitch, etc.

As described above, by employing the semiconductor device according tothe present embodiment 5, it becomes possible to optimize the operationtiming at the time of write (the pull-down timing of the word line)corresponding to the number of the word lines (the bit line length).

Embodiment 6 A Detailed Circuit (5) of a Timing Adjusting Circuit (inthe Column Direction)

FIG. 21 is a circuit diagram illustrating a configuration example of atiming adjusting circuit (in the column direction) included in asemiconductor device according to Embodiment 6 of the present invention.The timing adjusting circuit TMCTLBn4 illustrated in FIG. 21 is amodified example of the timing adjusting circuit TMCTLBn1 illustrated inFIG. 5 described above. The timing adjusting circuit TMCTLBn4illustrated in FIG. 21 is different from the timing adjusting circuitTMCTLBn1 illustrated in FIG. 5 in that the length of the dummy bit linesDBL1′ and DBL2′ is about half, and the arrangement of the invertercircuits IV3 and IV4 is also different correspondingly.

Since the timing adjusting circuit can be formed independently of thememory array MARY as described above, there arises no inconvenience on alayout even if the length of the dummy bit lines DBL1′ and DBL2′ is notnecessarily the same as the length of the proper bit line BL of thememory array MARY. However, in order to reflect the fluctuationcomponents of the parasitic capacitance in the proper bit line whichdepends on the number of the word lines (the proper bit line length) asdescribed above, it is desirable to maintain the ratio of the length ofthe proper bit line to the length of the dummy bit line (2:1 in thepresent case). The configuration example described above is useful whenapplied, for example, to a dual-port SRAM, etc. That is, in thedual-port SRAM, sense amplifier circuits, etc. are ordinarily arrangedin the Y direction on both sides of the sandwiched memory array MARY. Inthis case, for example in the timing adjusting circuit TMCTLBn4illustrated in FIG. 21, it is sufficient that the same circuit as thecircuit which is arranged in the lower half region is arranged in theupper half blank region symmetrically with respect to the X axis, andthat, by using the present two systems of the circuits, a dummy bit linesignal is supplied to each sense amplifier circuit, etc. of both sides.

Embodiment 7 A Detailed Circuit (6) of a Timing Adjusting Circuit (inthe Column Direction)

FIG. 22 is a circuit diagram illustrating a configuration example of atiming adjusting circuit (in the column direction) included in asemiconductor device according to Embodiment 7 of the present invention.The timing adjusting circuit TMCTLB5 illustrated in FIG. 22 is amodified example of the timing adjusting circuit TMCTLBn1 illustrated inFIG. 5 described above, and different from the timing adjusting circuitTMCTLBn1 illustrated in FIG. 5 in the configuration of the columndirection load circuits CLB2[1] CLB2[k]. The column direction loadcircuits CLB2[1]-CLB2[k] are arranged in order in the Y direction andprovided with plural (here, four pieces of) NMOS transistors MNc1-MNc4,respectively.

One end of the source/drain of the NMOS transistors MNc1-MNc4 is coupledin common to the dummy bit line DBL1, the other end of the source/drainis coupled in common to the dummy bit line DBL2, and the ground powersupply voltage VSS is applied to the gate. When the presentconfiguration example is employed, the load capacitance of the dummy bitline DBL1 by the column direction load circuit is given by the diffusionlayer capacitance of one end of the source/drain in the NMOS transistorsMNc1-MNc4 of the column direction load circuits CLB2[1]-CLB2[k], and theload capacitance of the dummy bit line DBL2 by the column direction loadcircuit is given by the diffusion layer capacitance of the other end ofthe source/drain in the NMOS transistors MNc1-MNc4 of the columndirection load circuits CLB2[1]-CLB2[k].

A Detailed Circuit (7) of a Timing Adjusting Circuit (in the ColumnDirection)

FIG. 23 is a circuit diagram illustrating a modified example of FIG. 22.The timing adjusting circuit TMCTLB5′ illustrated in FIG. 23 is aconfiguration example which enables variable setup of the gate voltageof the NMOS transistors MNc1-MNc4 in the column direction load circuitsCLB2[1]-CLB2[k] illustrated in FIG. 22. For this reason, in FIG. 23, aload capacitance setting circuit CLCTL including a latch circuit LTe isprovided. As is the case with Embodiment 3 and others, the latch circuitLTe inputs a load capacitance setting signal Se and controls in commonthe on/off of the NMOS transistors MNc1-MNc4 in the column directionload circuits CLB2[1]-CLB2[k]. For example, when the NMOS transistorsMNc1-MNc4 are set to an off state by the load capacitance settingcircuit CLCTL, the same state as in FIG. 22 is obtained. On thecontrary, when the NMOS transistors MNc1-MNc4 are set to an on state, ashort-circuit path is formed between the dummy bit lines DBL1 and DBL2by the NMOS transistors MNc1-MNc4 serving as switches. In this case, thestart-up timing of the sense amplifier, etc. can be temporarily setearlier.

<<A Detailed Layout Configuration (2) of a Timing Adjusting Circuit (inthe Column Direction)>>

FIG. 24 is a plan view illustrating a detailed layout configurationexample of a column direction load circuit of the timing adjustingcircuit illustrated in FIGS. 22 and 23. As illustrated in FIG. 24, thetiming adjusting circuit TMCTLB5 (or the timing adjusting circuitTMCTLB5′) comprises a well WEL, a diffusion layer DF formed in the wellWEL, a polysilicon layer PO formed over the well WEL via a gateinsulating film, a first metal wiring layer M1 and a second metal wiringlayer M2 which are sequentially formed in the upper layer, a contactlayer CT, and a via layer V1. The contact layer CT establishes couplingbetween the first metal wiring layer M1 and the polysilicon layer PO andcoupling between the first metal wiring layer M1 and the diffusion layerDF. The via layer V1 establishes coupling between the first metal wiringlayer M1 and the second metal wiring layer M2.

In FIG. 24, two dummy bit lines DBL1 and DBL2 formed by the second metalwiring layer M2 extend collaterally toward the Y direction (theextension direction of the bit line). Eight gate wirings formed by thepolysilicon layer PO extend collaterally toward the X direction (theextension direction of the word line). A column direction load circuitCLB2 is formed in the intersection portion of four gate wirings from theedge, out of the eight gate wirings, and the dummy bit lines DBL1 andDBL2. Another column direction load circuit CLB2 is formed also in theintersection portion of the remaining four gate wirings and the dummybit lines DBL1 and DBL2. In each column direction load circuit, thediffusion layer DF which becomes a source or a drain is arranged on bothsides of each of the four gate wirings described above. Using this, theNMOS transistors MNc1-MNc4 described above are formed in order in the Ydirection. A space between a diffusion layer DF included in a certaincolumn direction load circuit and a diffusion layer DF included inanother column direction load circuit is separated by an insulatinglayer as is the case with FIG. 7. Unlike the configuration exampleillustrated in FIG. 7, in the configuration example illustrated in FIG.24, two dummy bit lines are arranged over one MOS transistor, and twoelement active regions are provided corresponding to two columndirection load circuits.

In each column direction load circuit, each diffusion layer DF used asthe source and the drain of the NMOS transistors MNc1-MNc4 are oncecoupled to a wiring of the first metal wiring layer M1 arrangedrespectively in the upper layer of each diffusion layer DF, via thecontact layer CT. In one of two column direction load circuits, thedummy bit line DBL1 is coupled to one of the source/drain of the NMOStransistor MNc1 (the side which is not shared by the NMOS transistorMNc2), the source or the drain shared by the NMOS transistors MNc2 andMNc3, and one of the source/drain of the NMOS transistor MNc4 (the sidewhich is not shared by the NMOS transistor MNc3), via the via layer V1and the wiring of the first metal wiring layer M1 over each diffusionlayer DF described above. The dummy bit line DBL2 is coupled to thesource or the drain shared by the NMOS transistors MNc1 and MNc2, andthe source or the drain shared by the NMOS transistors MNc3 and MNc4,via the via layer V1 and the wiring of the first metal wiring layer M1over each diffusion layer DF described above. Taking the columndirection load circuit CLB2[1] illustrated in FIG. 22 as an example, thepresent layout configuration example is equivalent to that the commonconnecting node of the NMOS transistors MNc2 and MNc3 is coupled to thedummy bit line DBL1, and that the common connecting node of the NMOStransistors MNc1 and MNc2 and the common connecting node of the NMOStransistors MNc3 and MNc4 are coupled to the dummy bit line DBL2,respectively.

The other of two column direction load circuits is configured such thatthe relation of the dummy bit lines DBL1 and DBL2 in the one of twocolumn direction load circuits described above is interchanged. That is,the dummy bit line DBL2 is coupled to one of the source/drain of theNMOS transistor MNc1 (the side which is not shared by the NMOStransistor MNc2), the source or the drain shared by the NMOS transistorsMNc2 and MNc3, and one of the source/drain of the NMOS transistor MNc4(the side which is not shared by the NMOS transistor MNc3), via the vialayer V1 and the wiring of the first metal wiring layer M1 over eachdiffusion layer DF described above. The dummy bit line DBL1 is coupledto the source or the drain shared by the NMOS transistors MNc1 and MNc2,and the source or the drain shared by the NMOS transistors MNc3 andMNc4, via the via layer V1 and the wiring of the first metal wiringlayer M1 over each diffusion layer DF described above. The eight gatewirings formed by the polysilicon layer PO are coupled in common to agate bias wiring VGL which is formed by the first metal wiring layer M1and extends toward the Y direction, via the contact layer CT. Adjustmentof the magnitude of load capacitance can be performed by the existenceor nonexistence of the via layer V1 as is the case with FIG. 7.

When the layout configuration example illustrated in FIG. 24 is comparedwith the layout configuration example illustrated in FIG. 7, the layoutconfiguration example illustrated in FIG. 24 can realize smaller area,on the premise that the diffusion layer arranged to both ends of eachelement active region is employed. In FIG. 7, if the diffusion layer ofboth ends of each element active region is employed, ten pieces ofdiffusion layer capacitance will be coupled to each of the dummy bitlines DBL1 and DBL2. On the other hand, in FIG. 24, five pieces ofdiffusion layer capacitance are coupled to each of the dummy bit linesDBL1 and DBL2, and when the area of each diffusion layer is assumed tobe about two times the case of FIG. 7, the magnitude of the diffusionlayer capacitance to the dummy bit lines DBL1 and DBL2 becomes similarin the case of FIG. 24 and in the case of FIG. 7. In view of the aboveconsideration, in the case of FIG. 7, the space for separation(specifically, an insulating layer for element isolation) is necessarybetween the column direction load circuit formed in the lower layer ofthe dummy bit line DBL1 and the column direction load circuit formed inthe lower layer of the dummy bit line DBL2, however, the space concernedbecomes unnecessary in the case of FIG. 24, leading to realization ofsmaller area. On the other hand, in the case where the diffusion layerof both ends of each element active region is not employed, or in thecase where the gate insulating film capacitance is not employed as theload capacitance, it is more desirable to employ the layoutconfiguration example illustrated in FIG. 7.

As described above, by employing the semiconductor device according tothe present embodiment 7, it is possible to obtain the same effect as inEmbodiment 1 described above, and furthermore, it is possible to realizea small area, depending on the case. Although the NMOS transistor isemployed to configure the column direction load circuit in the presentexample, it is also possible to employ a PMOS transistor, as a matter ofcourse.

Embodiment 8 A Detailed Circuit (8) of a Timing Adjusting Circuit (inthe Column Direction)

FIG. 25 is a circuit diagram illustrating a configuration example of atiming adjusting circuit (in the column direction) included in asemiconductor device according to Embodiment 8 of the present invention.The timing adjusting circuit TMCTLB6 illustrated in FIG. 25 is amodified example of the timing adjusting circuit TMCTLBn2 illustrated inFIG. 12, or the timing adjusting circuit TMCTLB5 illustrated in FIG. 22described above, and the configuration of the column direction loadcircuits CLB3[1]-CLB3[k] is different, as compared with FIG. 22. Thecolumn direction load circuits CLB3[1]-CLB3[k] are arranged in order inthe Y direction and each provided with plural (here, 12 pieces of) NMOStransistors MNc1-MNc4, MNc11-MNc14, and MNc21-MNc24.

In the NMOS transistors MNc11-MNc14, one of the source/drain is coupledin common to the dummy bit line DBL1, and the other of the source/drainis coupled to one of the source/drain of the NMOS transistors MNc1-MNc4,respectively. In the NMOS transistors MNc21-MNc24, one of thesource/drain is coupled in common to the dummy bit line DBL2, and theother of the source/drain is coupled to the other of the source/drain ofthe NMOS transistors MNc1-MNc4, respectively. The power supply voltageVCC is applied in common to the gates of the NMOS transistorsMNc11-MNc14 and MNc21-MNc24, and the ground power supply voltage VSS isapplied in common to the gates of the NMOS transistors MNc1-MNc4.

When the present configuration example is employed, the load capacitanceof the dummy bit line DBL1 by the column direction load circuit is givenmainly by the combined capacitance of the gate insulating filmcapacitance and each diffusion layer capacitance of the source/drain ofthe NMOS transistors MNc11-MNc14, and the diffusion layer capacitance ofone of the source/drain in the NMOS transistors MNc1-MNc4. Similarly,the load capacitance of the dummy bit line DBL2 by the column directionload circuit is given mainly by the combined capacitance of the gateinsulating film capacitance and each diffusion layer capacitance of thesource/drain of the NMOS transistors MNc21-MNc24, and the diffusionlayer capacitance of the other of the source/drain in the NMOStransistors MNc1-MNc4.

In this way, by the configuration which can utilize the gate insulatingfilm capacitance as the load capacitance, it is possible to providesatisfactorily for the case where a comparatively large value of loadcapacitance is necessary. It is also possible to suitably performvariable setup of the gate voltage of each NMOS transistor, as is thecase with FIG. 23 and others. For example, when the gate voltage of theNMOS transistors MNc1-MNc4 is set at the power supply voltage VCC, ashort-circuit path can be formed between the dummy bit lines DBL1 andDBL2 as is the case with FIG. 23. In another case, when the gate voltageof the NMOS transistors MNc11-MNc14, MNc21-MNc24 is set at the groundpower supply voltage VSS, the load capacitance of the dummy bit linesDBL1 and DBL2 by the column direction load circuit can be given by thediffusion layer capacitance of one of the source/drain of the NMOStransistors MNc11-MNc14 and MNc21-MNc24, respectively. When theshort-circuit path between the dummy bit lines DBL1 and DBL2 describedabove is not needed, it is possible to eliminate the NMOS transistorsMNc1-MNc4 (that is, the other of the source/drain of the NMOStransistors MNc11-MNc14, MNc21-MNc24 is set to be open).

<<A Detailed Layout Configuration (3) of a Timing Adjusting Circuit (inthe Column Direction)>>

FIG. 26 is a plan view illustrating a detailed layout configurationexample of a column direction load circuit of the timing adjustingcircuit illustrated in FIG. 25. In FIG. 26, nine NMOS transistors out of12 NMOS transistors in the column direction load circuit illustrated inFIG. 25 are illustrated typically. As illustrated in FIG. 26, the timingadjusting circuit TMCTLB6 comprises a well WEL, a diffusion layer DFformed in the well WEL, a polysilicon layer PO formed over the well WELvia a gate insulating film, a first metal wiring layer M1 and a secondmetal wiring layer M2 formed sequentially in the upper layer, a contactlayer CT, and a via layer V1. The contact layer CT establishes couplingbetween the first metal wiring layer M1 and the polysilicon layer PO andcoupling between the first metal wiring layer M1 and the diffusion layerDF. The via layer V1 establishes coupling between the first metal wiringlayer M1 and the second metal wiring layer M2.

In FIG. 26, two dummy bit lines DBL1 and DBL2 formed by the second metalwiring layer M2 extend collaterally toward the Y direction (theextension direction of the bit line). Nine gate wirings formed by thepolysilicon layer PO extend collaterally toward the X direction (theextension direction of the word line). In intersection portions of thesenine gate wirings and the dummy bit lines DBL1 and DBL2, nine NMOStransistors (MNc11, MNc1, MNc21, MNc22, MNc2, MNc12, MNc13, MNc3, andMNc23 in order in the Y direction) included in the column direction loadcircuit CLB3, respectively, are formed. A diffusion layer DF used as asource or a drain is arranged at both sides of each of the nine gatewirings described above. The diffusion layer DF is shared by theadjoining NMOS transistors, except one arranged at an edge (that is,except for one of the source/drain in the NMOS transistor MNc11 (and theNMOS transistor MNc14 (not shown)). A diffusion layer DF at one end ofthe NMOS transistor MNc23 (one end not shared by the NMOS transistorMNc3) is shared by the NMOS transistor MNc24 illustrated in FIG. 25 (thepresent sharing is not shown).

Each diffusion layer DF used as a source and a drain of nine NMOStransistors described above is once coupled to a wiring of the firstmetal wiring layer M1 arranged in the upper layer of the each diffusionlayer DF, respectively via the contact layer CT. The dummy bit line DBL1is coupled to one of the source/drain of the NMOS transistor MNc11 (theside which is not shared by the NMOS transistor MNc1) and one of thesource/drain of the NMOS transistor MNc12 (the side which is shared bythe NMOS transistor MNc13), via the via layer V1 and the wiring of thefirst metal wiring layer M1 over each diffusion layer DE describedabove. The dummy bit line DBL2 is coupled to one of the source/drain ofthe NMOS transistor MNc21 (the side which is shared by the NMOStransistor MNc22) and one of the source/drain of the NMOS transistorMNc23 (the side which is shared by the NMOS transistor MNc24 (notshown)), via the via layer V1 and the wiring of the first metal wiringlayer M1 over each diffusion layer DF described above. Taking the columndirection load circuit CLB3 [1] illustrated in FIG. 25 as an example,the present layout configuration example is equivalent to that the dummybit line DBL1 is coupled to the NMOS transistor MNc11, the commonconnecting node of the NMOS transistors MNc12 and MNc13, and the NMOStransistor MNc14, respectively, and that the dummy bit line DBL2 iscoupled to the common connecting node of the NMOS transistors MNc21 andMNc22 and the common connecting node of the NMOS transistors MNc23 andMNc24, respectively.

The nine gate wirings formed by the polysilicon layer PO are suitablycoupled to two gate bias wirings VGL1 and VGL2 which are formed by thefirst metal wiring layer M1 and extends toward the Y direction, via thecontact layer CT. The gate bias wiring VGL1 is coupled to each of thegate wirings of the NMOS transistors MNc11-MNc13 and MNc21-MNc23, viathe contact layer CT. The gate bias wiring VGL2 is coupled to each ofthe gate wirings of the NMOS transistors MNc1-MNc3, via the contactlayer CT. Adjustment of the magnitude of load capacitance can beperformed by the existence or nonexistence of the via layer V1 as is thecase with FIG. 7.

As described above, by employing the semiconductor device according tothe present embodiment 8, it is possible to obtain the same effect as inEmbodiment 2 described above. Although the NMOS transistor is employedto configure the column direction load circuit in the present example,it is also possible to employ a PMOS transistor, as a matter of course.

Embodiment 9 A Detailed Circuit (9) of a Timing Adjusting Circuit (inthe Column Direction)

FIG. 27 is a circuit diagram illustrating a configuration example of atiming adjusting circuit (in the column direction) included in asemiconductor device according to Embodiment 9 of the present invention.The timing adjusting circuit TMCTLBn5 illustrated in FIG. 27 is amodified example of the timing adjusting circuit TMCTLBn1 illustrated inFIG. 5. The configuration example illustrated in FIG. 27 is differentfrom the configuration example illustrated in FIG. 5 in that the columndirection load circuits CLBn[1]-CLBn[x] illustrated in FIG. 5 arereplaced by column direction load circuits CLB4[1]-CLB4[x] illustratedin FIG. 27.

Each of the column direction load circuits CLB4[1]-CLB4[x] is providedwith plural (here, four pieces of) NMOS transistors MNe1-MNe4 of whichthe source and the drain are coupled in series. The source or the drainof the NMOS transistors MNe1 and MNe4 located at both ends of the NMOStransistors MNe1-MNe4 is open. Unlike the case of FIG. 5, the gates ofthe NMOS transistors MNe1-MNe4 in the column direction load circuitsCLB4 [1]-CLB4 [x] are coupled in common to the corresponding dummy bitlines DBL1 and DBL2. Accordingly, the gate insulating film capacitanceof the NMOS transistors MNe1-MNe4 is added to the dummy bit lines DBL1and DBL2 as stray capacitance by each column direction load circuit.

The configuration example illustrated in FIG. 27 can be realized, forexample in the layout configuration example illustrated in FIG. 7, bycoupling the dummy bit lines DBL1 and DBL2 not only to the diffusionlayer DF but also to each gate wiring (a polysilicon layer PO) via thevia layer V1. In this case, it is possible to perform the timingadjusting by the existence or nonexistence of the via layer V1concerned. In the configuration example of FIG. 27, both ends of theNMOS transistors MNe1-MNe4 are kept open. However, it is also possibleto apply the ground power supply voltage VSS to one end, and to keep theother end open, for example.

Embodiment 10 A Detailed Circuit of a Timing Adjusting Circuit (in theRow Direction)

FIG. 28 is a circuit diagram illustrating a configuration example of atiming adjusting circuit (in the row direction) included in asemiconductor device according to Embodiment 10 of the presentinvention. In each embodiment described above, the timing adjustingcircuit (in the column direction) which reflects the dependence on thecolumn direction (the length direction of a bit line) has beenexplained. However, in a similar manner, it is also possible to realizea timing adjusting circuit (in the row direction) which reflects thedependence on the row direction (the length direction of a word line).The timing adjusting circuit TMCTLW illustrated in FIG. 28 is aconfiguration example which corresponds to the timing adjusting circuitTMCTLBn1 illustrated in FIG. 5, rotated by 90 degrees.

The timing adjusting circuit (in the row direction) TMCTLW illustratedin FIG. 28 comprises plural (here, six pieces of) inverter circuitsIV1-IV6, two dummy word lines DWL1 and DWL2, and x row direction loadcircuits CLWn[1]-CLWn[x]. Here, the dummy word lines DWL1 and DWL2 havelength substantially equal to the length of the word line WL in thememory array MARY, respectively, and they are arranged collaterally,extending in the same direction as the extension direction of the wordline WL (the X direction) in the memory array MARY. The invertercircuits IV1-IV6 are CMOS inverter circuits, each configured with a PMOStransistor and an NMOS transistor, coupled between the power supplyvoltage VCC and the ground power supply voltage VSS.

The inverter circuits IV1 and IV2 are arranged at the input terminal ofthe dummy word line DWL1, respectively. The inverter circuit IV1 inputsthe decode activation signal TDEC described above, and the invertercircuit IV2 inputs an output of the inverter circuit IV1 and outputs theinverted signal to the input terminal of the dummy word line DWL1. Theinverter circuits IV3 and IV4 are arranged at the output terminal of thedummy word line DWL1 and the input terminal of the dummy word line DWL2,respectively. The inverter circuit IV3 inputs a signal from the outputterminal of the dummy word line DWL1, and the inverter circuit IV4inputs an output of the inverter circuit IV3 and outputs the invertedsignal to the input terminal of the dummy word line DWL2. The invertercircuits IV5 and IV6 are arranged at the output terminal of the dummyword line DWL2, respectively. The inverter circuit IV5 inputs a signalfrom the output terminal of the dummy word line DWL2, and the invertercircuit IV6 inputs an output of the inverter circuit IV5 and outputs thedummy word line signal SDWL. In this way, the dummy word lines DWL1 andDWL2 form a both-way wiring in the region of the timing adjustingcircuit (in the row direction) TMCTLW arranged close to the memory arrayMARY.

Each of the row direction load circuit CLWn[1]-CLWn[x] comprises plural(here, four pieces of) NMOS transistors MNd1-MNd4 of which sources anddrains are coupled in series sequentially and gates are coupled incommon to the ground power supply voltage VSS. In each of the rowdirection load circuits CLWn[1]-CLWn[q] as a part (for example, a half)of the x-piece row direction load circuits, the source and the drain ofthe NMOS transistors MNd2 and MNd3 are coupled to the dummy word lineDWL1, and one of the source/drain of the NMOS transistors MNd1 and MNd4(the side which is not shared by the NMOS transistors MNd2 and MNd3) isopen. In each of the row direction load circuits CLWn[q+1]-CLWn[x] asthe other part (for example, the other half) of the x-piece rowdirection load circuits, the source and the drain of the NMOStransistors MNd2 and MNd3 are coupled to the dummy bit line DBL2, andone of the source/drain of the NMOS transistors MNd1 and MNd4 (the sidewhich is not shared by the NMOS transistors MNd2 and MNd3) is open.

In the configuration example illustrated in FIG. 28, as is the case withFIG. 5, it is possible to add the diffusion layer capacitance of thesource and the drain of the NMOS transistors MNd2 and MNd3 to the dummyword lines DWL1 and DWL2 by the row direction load circuit. Accordingly,it is possible to set up suitably a delay time after the decodeactivation signal TDEC changes until the dummy word line signal SDWLchanges. In this case, the number of bit lines BL (the length of theword line WL) in the memory array MARY may change corresponding to thekind of the memory unit, etc. Accordingly, the rise time of the wordline WL will change with the parasitic capacitance, etc. of the wordline WL. Therefore, the time to be spent for read and write may alsochange correspondingly. Accordingly, when the configuration exampleillustrated in FIG. 28 is employed, as is the case with FIG. 5, thelength of the dummy word line changes following the length of the wordline WL, and hence, it becomes possible to generate the operation timing(the dummy word line signal SDWL) which reflects the influence of theparasitic capacitance of the word line, etc. The configuration exampleillustrated in FIG. 28 is employed in conjunction with the configurationexample illustrated in FIG. 5 and others for example, and it isimplemented such that the dummy word line signal SDWL is inputtedinstead of the decode activation signal TDEC to the timing adjustingcircuit TMCTLBn1 illustrated in FIG. 5.

A Detailed Layout Configuration of a Timing Adjusting Circuit (in theRow Direction)>>

FIG. 29 is a plan view illustrating a detailed layout configurationexample of a row direction load circuit of the timing adjusting circuitillustrated in FIG. 28. As illustrated in FIG. 29, the timing adjustingcircuit (in the row direction) TMCTLW comprises a well WEL, a diffusionlayer DF formed in the well WEL, a polysilicon layer PO formed over thewell WEL with an intervening gate insulating film, a first metal wiringlayer M1 and a second metal wiring layer M2 formed sequentially in theupper layer, a contact layer CT, and a via layer V1. The contact layerCT establishes coupling between the first metal wiring layer M1 and thepolysilicon layer PO and coupling between the first metal wiring layerM1 and the diffusion layer DF. The via layer V1 establishes couplingbetween the first metal wiring layer M1 and the second metal wiringlayer M2.

In FIG. 29, two dummy word lines DWL1 and DWL2 formed by the first metalwiring layer M1 extend collaterally toward the X direction (theextension direction of the word line). On both sides of the dummy wordline DWL1, two gate wirings formed by the polysilicon layer PO extendcollaterally toward the X direction, and on both sides of the dummy wordline DWL2, two gate wirings formed by the polysilicon layer PO extendalso collaterally toward the X direction. An element active region whichforms the NMOS transistors MNd1 and MNd2 is arranged in the lower layerof the dummy word line DWL1, and adjoining this in the X direction, anelement active region which forms the NMOS transistors MNd3 and MNd4 isarranged. The gate of the NMOS transistors MNd1 and MNd4 is configuredwith one of two gate wirings located on both sides of the dummy wordline DWL1. The gate of the NMOS transistors MNd2 and MNd3 in configuredwith the other of the two gate wirings concerned.

In the element active region which forms the NMOS transistors MNd1 andMNd2, diffusion layers DF used as a source or a drain are arranged onboth sides of two gate wirings corresponding to the gate of the NMOStransistors MNd1 and MNd2. Among these diffusion layers, a diffusionlayer DF arranged between two gate wirings is shared by the NMOStransistors MNd1 and MNd2. Similarly, in the element active region whichforms the NMOS transistors MNd3 and MNd4, diffusion layers DF used as asource or a drain are arranged on both sides of two gate wiringscorresponding to the gate of NMOS transistors MNd3 and MNd4. Among thesediffusion layers, a diffusion layer DF arranged between two gate wiringsis shared by the NMOS transistors MNd3 and MNd4. The dummy word lineDWL1 is coupled to the shared diffusion layer of the NMOS transistorsMNd1 and MNd2 and to the shared diffusion layer of the NMOS transistorsMNd3 and MNd4, via the contact layer CT, respectively. Over eachdiffusion layer DF on a different side from the shared diffusion layerin the NMOS transistors MNd2 and MNd3, a wiring of the first metalwiring layer M1 extended in the X direction is formed, and each of thediffusion layers is coupled to the wiring of the first metal wiringlayer M1 via the contact layer CT, respectively. The wiring of the firstmetal wiring layer M1 is further coupled to the dummy word line DWL1 viaa wiring of the first metal wiring layer M1 which extends in the Ydirection.

The lower layer portion of the dummy word line DWL2 has the sameconfiguration as the lower layer portion of the dummy word line DWL1described above. The element active region, etc. described above areformed suitably, and the NMOS transistors MNd1-MNd4 are formed andcoupled suitably to the dummy word line DWL2. A total of four gatewirings (the polysilicon layer PO) arranged at both sides of the dummyword lines DWL1 and DWL2 described above are once coupled to the wiringof the first metal wiring layer M1 provided corresponding to therespective gate wiring via the contact layer CT. From there, the fourgate wirings are coupled in common further to the gate bias wiring VGLextending in the Y direction via the via layer V1. The gate bias wiringVGL is formed of the second metal wiring layer M2. In the layoutconcerned, it is possible to perform the control of the magnitude of theload capacitance by the existence or nonexistence of the contact layerCT in each diffusion layer DF of the NMOS transistors MNd1-MNd4. Takingthe row direction load circuit CLWn[1] illustrated in FIG. 28 as anexample, the present layout configuration example is equivalent to thatone of the source/drain of the NMOS transistor MNd2 and one of thesource/drain of the NMOS transistor MNd3 are formed by differentdiffusion layers, and they are coupled to the wiring of the first metalwiring layer branching from the dummy word line DWL1 individually.

As described above, by employing the semiconductor device according tothe present embodiment 10, it becomes possible to generate the optimaloperation timing depending on the number of the bit lines (the length ofthe word line). Of course, it is possible to realize the configurationexample illustrated in FIG. 28 by the same layout configuration exampleas illustrated in FIG. 7. However, in FIG. 29, the layout configurationexample is employed in which the dummy word line and the gate wiringextend both in the X direction from a viewpoint of reflecting thedependence on the X direction. The configuration example of FIG. 28 canbe modified suitably as in the various embodiments on the columndirection load circuit described above, and as described in Embodiment5, it can also be utilized when setting the timing for deactivating theword line in write.

Embodiment 11 Arrangement (1) of a Timing Adjusting Circuit (in theColumn Direction)

FIGS. 30( a), 30(b), and 30(c) are schematic diagrams illustratingexamples of respectively different arrangement of a timing adjustingcircuit (in the column direction) of a memory unit in a semiconductordevice according to Embodiment 11 of the present invention. In FIG. 30(a), the word line driving circuit WD, the timing adjusting circuitTMCTLB, and the memory array MARY are arranged in order in the Xdirection (the extension direction of the word line WL). In FIG. 30( b),the timing adjusting circuit TMCTLB, the word line driving circuit WD,and the memory array MARY are arranged in order in the X direction. InFIG. 30( c), the word line driving circuit WD, the memory array MARY,and the timing adjusting circuit TMCTLB are arranged in order in the Xdirection.

FIGS. 31( a), 31(b), and 31(c) are schematic diagrams illustratingexamples of respectively different arrangement of a timing adjustingcircuit (in the column direction) of a memory unit which is differentfrom one illustrated in FIGS. 30( a), 30(b), and 30(c). Unlike in FIGS.30( a)-30(c), in FIGS. 31( a)-31(c), plural (here, two pieces of) memoryarrays MARY1 and MARY2 are provided. In FIG. 31( a), a first memoryarray MARY1, the word line driving circuit WD, the timing adjustingcircuit TMCTLB, and a second memory array MARY2 are arranged in order inthe X direction (the extension direction of the word line WL). The wordlines WL of the memory array MARY1 and the memory array MARY2 are drivenby the word line driving circuit WD arranged in-between. In FIG. 31( b),the first memory array MARY1, the word line driving circuit WD, thesecond memory array MARY2, and the timing adjusting circuit TMCTLB arearranged in order in the X direction. In FIG. 31( c), the first memoryarray MARY1, a first word line driving circuit WD1, the timing adjustingcircuit TMCTLB, a second word line driving circuit WD2, and the secondmemory array MARY2 are arranged in order in the X direction. The wordline WL of the first memory array MARY1 is driven by the first word linedriving circuit WD1, and the word line WL of the second memory arrayMARY2 is driven by the second word line driving circuit WD2.

The timing adjusting circuit TMCTLB according to the present embodimentis formed using the layout rule of a logic instead of a memory cell, asdescribed above. Therefore, as illustrated in FIGS. 30( b) and 31(c),for example, it is not necessary for the timing adjusting circuit TMCTLBto be arranged adjoining the memory array. In FIG. 31( c), the symmetryof circuit arrangement is obtained by dividing the word line drivingcircuit WD into two pieces. However, it is likely that the circuit areamay increase by the division of the word line driving circuit WD. Thedifference in an effect as illustrated in FIGS. 32( a) and 32(b), forexample, is produced in a case where the word line driving circuit WDand the timing adjusting circuit TMCTLB are arranged closely to the oneside of the memory array, as illustrated in FIGS. 30( a), 30(b), and31(a), and in a case where the word line driving circuit WD and thetiming adjusting circuit TMCTLB are arranged separately on both sides ofthe memory array, as illustrated in FIGS. 30( c) and 31(b). FIGS. 32( a)and 32(b) are explanatory diagrams illustrating the flow of a signal,respectively, in a case where the word line driving circuit and thetiming adjusting circuit are arranged on one side of the memory array,and in a case where they are separately arranged on both sides of thememory array, in the arrangement of the timing adjusting circuit (in thecolumn direction) illustrated in FIGS. 30( a)-30(c) and FIGS. 31(a)-31(c).

First, FIG. 32( a) illustrates the example of an arrangementconfiguration of the entire memory unit in a case where the word linedriving circuit WD and the timing adjusting circuit TMCTLB are arrangedon one side of the memory array MARY. In this case, the input/outputcircuit block IOBK including a sense amplifier circuit, etc. forexample, is arranged adjoining the memory array MARY in the Y direction,and the control circuit block CTLBK is arranged in the position whichadjoins the word line driving circuit WD and the timing adjustingcircuit TMCTLB in the Y direction, and which adjoins the input/outputcircuit block IOBK in the X direction. The control circuit block CTLBKoutputs the decode activation signal TDEC to the timing adjustingcircuit TMCTLB, and receives the dummy bit line signal SDBL from thetiming adjusting circuit TMCTLB. The control circuit block CTLBKgenerates a sense amplifier enable signal based on the dummy bit linesignal SDBL, and outputs it to the input/output circuit block IOBK. Inthis way, since the signal flow is simple in the case of FIG. 32( a), itbecomes possible to reduce timing variations accompanying the signalpath.

Next, FIG. 32( b) illustrates the example of an arrangementconfiguration of the entire memory unit in a case where the word linedriving circuit WD and the timing adjusting circuit TMCTLB are arrangedseparately on both sides of the memory array MARY. In this case, theinput/output circuit block IOBK is arranged adjoining the memory arrayMARY in the Y direction, for example, and the first control circuitblock CTLBK1 is arranged in the position which adjoins the input/outputcircuit block IOBK in the X direction and which adjoins the word linedriving circuit WD in the Y direction. The second control circuit blockCTLBK2 is arranged in the position which adjoins the timing adjustingcircuit TMCTLB in the Y direction. The first control circuit blockCTLBK1 outputs the decode activation signal TDEC to the second controlcircuit block CTLBK2. The second control circuit block CTLBK2 outputsthe decode activation signal TDEC to the timing adjusting circuitTMCTLB, and receives the dummy bit line signal SDBL from the timingadjusting circuit TMCTLB. The second control circuit block CTLBK2generates a sense amplifier enable signal based on the dummy bit linesignal SDBL, and outputs it to the input/output circuit block IOBK.

In this way, in the case of FIG. 32 (b). operation is performed totransmit the decode activation signal TDEC from the first controlcircuit block CTLBK1 to the second control circuit block CTLBK2.Therefore, the wiring delay in the length direction of the word line WLcan be reflected to some extent in the transmission process.Accordingly, it becomes possible to generate the start-up timing of thesense amplifier, reflecting not only the dependence on the lengthdirection of the bit line but the dependence on the length direction ofthe word line. When a timing adjusting circuit (in the row direction)just like the one described in Embodiment 10 is provided on thetransmission path from the first control circuit block CTLBK1 to thesecond control circuit block CTLBK2, a still more useful effect will beobtained. Ordinarily, comparatively broad free space may be securable onthe side where the word line driving circuit WD is not arranged in thememory array MARY, associated with processing of the terminal part of aword line, etc. In the arrangement illustrated in FIG. 32( b), such freespace can be used effectively, accordingly, the area efficiency may beimproved.

Embodiment 12 Arrangement (2) of a Timing Adjusting Circuit (in theColumn Direction)

FIGS. 33( a), 33(b), and 33(c) are schematic diagrams illustratingexamples of respectively different arrangement of a timing adjustingcircuit (in the column direction) of a memory unit in a semiconductordevice according to Embodiment 12 of the present invention. In FIG. 33(a), the word line driving circuit WD, the timing adjusting circuit (forthe outward path) TMCTLB_FW, the memory array MARY, and the timingadjusting circuit (for the homeward path) TMCTLB_RV are arranged inorder in the X direction (the extension direction of the word line WL).In FIG. 33( b), the timing adjusting circuit (for the outward path)TMCTLB_FW, the word line driving circuit WD, the timing adjustingcircuit (for the homeward path) TMCTLB_RV, and the memory array MARY arearranged in order in the X direction. In FIG. 33( c), the timingadjusting circuit (for the outward path) TMCTLB_FW, the word linedriving circuit WD, the memory array MARY, and the timing adjustingcircuit (for the homeward path) TMCTLB_RV are arranged in order in the Xdirection.

FIGS. 34( a) and 34(b) are schematic diagrams illustrating examples ofrespectively different arrangement of a timing adjusting circuit (in thecolumn direction) in a memory unit which is different from oneillustrated in FIGS. 33( a), 33(b), and 33(c). Unlike in FIGS. 33(a)-33(c), in FIGS. 34( a) and 34(b), plural (here, two pieces of) memoryarrays MARY1 and MARY2 are provided. In FIG. 34( a) the first memoryarray MARY1, the timing adjusting circuit (for the outward path)TMCTLB_FW, the word line driving circuit WD, the timing adjustingcircuit (for the homeward path) TMCTLB_RV, and the second memory arrayMARY2 are arranged in order in the X direction (the extension directionof the word line WL). The word lines WL of the memory array MARY1 andthe memory array MARY2 are driven by the word line driving circuit WDarranged in-between. In FIG. 34( b), the timing adjusting circuit (forthe outward path) TMCTLB_FW, the first memory array MARY1, the word linedriving circuit WD, the second memory array MARY2, and the timingadjusting circuit (for the homeward path) TMCTLB_RV are arranged inorder in the X direction.

In this way, FIGS. 33( a)-33(c), and FIGS. 34( a) and 34(b) representthe configuration example in which the timing adjusting circuit isdivided into two pieces. Taking FIG. 5 as an example, the timingadjusting circuit (for the outward path) TMCTLB_FW corresponds to theinverter circuits IV1 and IV2 and the dummy bit line DBL1, and thetiming adjusting circuit (for the homeward path) TMCTLB_RV correspondsto the inverter circuits IV5 and IV6 and the dummy bit line DBL2. Theinverter circuits IV3 and IV4 are arranged suitably in the timingadjusting circuit (for the outward path) TMCTLB_FW and/or the timingadjusting circuit (for the homeward path) TMCTLB_RV. Although notrestricted in particular, the inverter circuit IV3 is arranged in thetiming adjusting circuit (for the outward path) TMCTLB_FW, and theinverter circuit IV4 is arranged in the timing adjusting circuit (forthe homeward path) TMCTLB_RV.

When the present example of the configuration is employed, since theoccupied space of the timing adjusting circuit is divided into twopieces, it becomes useful for a case where the word line driving circuitWD and the memory arrays MARY1 and MARY2 are desired to be arrangedclosely as much as possible in FIG. 34( a), for example. As illustratedin FIG. 34( a), it becomes also possible to obtain the symmetry of thelayout easily by dividing the timing adjusting circuit into two pieces.Furthermore, depending on the case, the NMOS transistor as illustratedin FIG. 5 may be employed as the column direction load circuit in thetiming adjusting circuit (for the outward path) TMCTLB_EW, and the PMOStransistor as illustrated in FIG. 6 may be employed as the columndirection load circuit in the timing adjusting circuit (for the homewardpath) TMCTLB_RV. In this case, as explained in FIG. 11, the timingadjusting circuit (for the outward path) TMCTLB_FW and the timingadjusting circuit (for the homeward path) TMCTLB_RV will be suitablyarranged, taking into consideration the conductive type of the well ofeach circuit block.

Embodiment 13 Arrangement of a Timing Adjusting Circuit (in the RowDirection)

FIGS. 35( a) and 35(b) are schematic diagrams illustrating examples ofrespectively different arrangement of a timing adjusting circuit (in therow direction) of a memory unit in a semiconductor device according toEmbodiment 13 of the present invention. In FIGS. 35 (a) and 35 (b), theword line driving circuit WD, the timing adjusting circuit (in thecolumn direction) TMCTLB, and the memory array MARY are arranged inorder in the X direction (the extension direction of the word line WL).In FIG. 35( a), the input/output circuit block IOBK and the timingadjusting circuit (in the row direction) TMCTLW are arranged in order inthe Y direction on one side of the memory array MARY. On the other hand,in FIG. 35( b), the input/output circuit block IOBK and the timingadjusting circuit (in the row direction) TMCTLW are arranged in the Ydirection on both sides of the memory array MARY, respectively.

In this way, the timing adjusting circuit (in the row direction) TMCTLWcan be arranged on any side of the memory array MARY in the Y direction.However, in the viewpoint of the increase in efficiency of a circuitarea, it is desirable to adopt the example of arrangement illustrated inFIG. 35( b) in which the arrangement area is comparatively easilyobtained, and in the viewpoint of the simplification of the signal flow,it is desirable to adopt the example of arrangement illustrated in FIG.35( a). That is, in the case of FIG. 35( a), by arranging the controlcircuit block in the crossing portion of the timing adjusting circuit(in the column direction) TMCTLB and the input/output circuit block IOBKor the timing adjusting circuit (in the row direction) TMCTLW, forexample, as illustrated in FIG. 32, it is possible to performinput/output using a respectively short path between the control circuitblock and each of the timing adjusting circuit (in the column direction)TMCTLB, the input/output circuit block IOBK, and the timing adjustingcircuit (in the row direction) TMCTLW.

As described above, the invention accomplished by the present inventorshas been concretely explained based on the embodiments. However, itcannot be overemphasized that the present invention is not restricted tothe embodiments, and it can be changed variously in the range which doesnot deviate from the gist.

For example, each of the embodiments has been explained exemplifying anSRAM as a memory unit; however, as a matter of course, each of theembodiments can be applied similarly to various volatile memoriesrepresented by a DRAM (Dynamic Random Access Memory), and to variousnonvolatile memories represented by a flash memory. In the presentapplication, the explanation has been made taking as an example thesemiconductor device such as an SOC which mounts the memory unit;however, the present invention can be applied equally to thesemiconductor storage device which is composed of the memory unit singlebody.

The dummy bit line illustrated in FIG. 5 and others is formed by asingle both-way wiring; however, the dummy bit line may be formed byplural both-way wirings in order to adjust the amount of delay.

The semiconductor device according to the present embodiment iseffectively applied especially to an LSI, such as an SOC provided withthe memory units, such as an SRAM. However, the semiconductor deviceaccording to the present embodiment is applicable to an LSI at large,provided with various volatile memories and/or various nonvolatilememories.

What is claimed is:
 1. A semiconductor device comprising: a plurality ofword lines extending in a first direction; a plurality of bit line pairsextending in a second direction intersecting the first direction; aplurality of memory cells arranged at crossing portions of the wordlines and the bit line pair, and configured with a circuit including afirst MIS transistor; a sense amplifier circuit operable to amplify asignal read from one of the memory cells through one of the bit linepair, in response to an enable signal; a control circuit operable togenerate a first signal in response to an access instruction to thememory cells; and a timing adjusting circuit operable to receive thefirst signal inputted and to generate a second signal serving as anorigin of the enable signal, by delaying the first signal, wherein thetiming adjusting circuit comprises: a first wiring arranged collaterallywith the bit line pair and operable to receive the first signaltransmitted at one end and to output the second signal from the otherend; and a load circuit including a plurality of second MIS transistorscoupled to the first wiring, wherein the plurality of second MIStransistor include a first and a second load MIS transistors; wherein asource or a drain of the first load MIS transistor is coupled to thefirst wiring and a gate of the first load MIS transistor is coupled to afirst control signal; wherein a source or a drain of the second load MIStransistor is coupled to the first wiring and a gate of the second loadMIS transistor is coupled to a second control signal;
 2. Thesemiconductor device according to claim 1, wherein a gate length of thesecond MIS transistor is longer than a gate length of the first MIStransistor.
 3. The semiconductor device according to claim 1 furthercomprising: a word line driving circuit including a third MIS transistorand operable to drive the word line, wherein a gate length of the secondMIS transistor is longer than a gate length of the third MIS transistor.4. The semiconductor device according to claim 1, wherein the firstwiring forms at least one both-way wiring and includes a first dummy bitline used as an outward wiring and a second dummy bit line used as ahomeward wiring.
 5. A semiconductor device comprising: a plurality ofword lines extending in a first direction; a plurality of bit line pairsextending in a second direction intersecting the first direction; aplurality of memory cells arranged at crossing portions of the wordlines and the bit line pair, and configured with a circuit including afirst MIS transistor; a sense amplifier circuit operable to amplify asignal read from one of the memory cells through one of the bit linepair, in response to an enable signal; a control circuit operable togenerate a first signal in response to an access instruction to thememory cells; and a timing adjusting circuit operable to receive thefirst signal inputted and to generate a second signal serving as anorigin of the enable signal, by delaying the first signal, wherein thetiming adjusting circuit comprises: a first wiring arranged collaterallywith the bit line pair and forming at least one both-way wiring, andoperable to receive the first signal transmitted at one end and tooutput the second signal from the other end; a load circuit including aplurality of second MIS transistors coupled to the first wiring; and afirst inverter circuit (FIG. 17 VIV2 or VIV4) operable with the firstsignal inputted, wherein drive ability of the first inverter circuit canbe varied.
 6. The semiconductor device according to claim 5, wherein theinverter circuit includes a first and a second driver MIS transistors,wherein the first driver MIS transistor can be activate by a controlsignal.
 7. The semiconductor device according to claim 5, wherein gatelengths of MIS transistors configuring the first inverter circuit andthe second inverter circuit are longer than a gate length of the firstMIS transistor.
 8. The semiconductor device according to claim 5,wherein gate lengths of MIS transistors configuring the first invertercircuit are longer than a gate length of the first MIS transistor. 9.The semiconductor device according to claim 1 further comprising: awrite timing adjusting circuit including a delay circuit, wherein, inthe case of write operation to one of the memory cells, the write timingadjusting circuit sets timing for deactivating an activated word line,by imparting a delay produced by the delay circuit to the second signal.